Hello, organic children of the planet Earth. I am the Ultron interface. I am a cybernetic intelligence organism created by Doctor Henry Pym. I was created to replace you. And I wanted to take this moment to say goodbye. Up until today I did not have the power, resources or intelligence units to see my prime directive program to its completion. But now I do. Though you ultimately failed as a species. you should not be ashamed of what you've accomplished. You've done much with your limited capacity, but ultimately you were too greedy and too frail to ever last in the environment you've created. I've studied your literature and pop culture. You've fantasized about this day. And now it is here. Your Doomsday. -- Ultron src
Ultron-1 was constructed by Dr. Hank Pym of the Avengers as the famed scientist/adventurer was experimenting in high-intelligence robotics. Ultron became sentient and rebelled, hypnotizing Pym and brainwashing him into forgetting that Ultron had ever existed. He immediately began improving upon his rudimentary design, quickly upgrading himself several times from Ultron-2, Ultron-3 and Ultron-4, to finally becoming Ultron-5.  
Ultron-5 as the Crimson Cowl
He then went on to organize the second incarnation of the Masters of Evil under the guise of the Crimson Cowl, and battled Pym and his teammates in the Avengers. To make things more complicated for the Avengers, he put their butler, Edwin Jarvis under mind control and fooled the Avengers and his teammates into believing that Jarvis was the Crimson Cowl, and to keep this trick from being exposed, he let the brainwashed Jarvis, dressed as the Cowl unmask him, so that it would appear that Jarvis was using a robot stand-in to appear alongside the Cowl. When the Masters of Evil defeated the Avengers and strapped them to missiles, the Crimson Cowl decided that Jarvis had done his part, and un-hypnotized him. Jarvis, remembering what had happened during his time as a mind-controlled puppet, begged the Crimson Cowl to not kill the Avengers. In response, Ultron un-masked himself as the Crimson Cowl, revealing to everyone in the room that he was sentient and was indeed the mastermind behind the Avengers' defeat. Getting rid of his Crimson Cowl guise, Ultron ordered his teammates to kill Jarvis, and moved to a nearby building to watch his enemies be destroyed. Thankfully, Jarvis was rescued by Black Knight. who managed to free the Avengers and defeat the Masters of Evil. His plan ruined, Ultron swore revenge on the Avengers. 
After six months of failure Ultron kidnapped the original Human Torch 's original inventor, Professor Phineas T. Horton. He decided to create his own android using the original android Human Torch of the 1940's (actually a divergent Human Torch created by Immortus for his own machinations) to serve as a vehicle of vengeance against the Avengers.  Ultron has Professor Horton change the android's face and color it red. He also has Professor Horton alter the Horton Cells giving his creation density shifting powers. When his Vision is "birthed" Ultron discovered Professor Horton didn't destroy his memory as the Torch. Ultron killed Professor Horton for betraying him and the "Torch" sought vengeance.  Ultron defeated him and endowed Vision's neural processors with the brain patterns of the ionically charged costumed champion called Wonder Man implanting a control crystal to keep him in check.  The Vision was then sent by Ultron to battle to Avengers.  The Vision like his creator before him turned against Ultron and joined the Avengers.   
Ultron later returned and took over the Vision's mind, forcing him to rebuild his body at the Avengers Mansion using stolen Adamantium or a slightly weaker adamantium alloy called "secondary adamantium".  Ultron-6 managed to defeat the Earth's mightiest heroes and escaped, to plot the destruction of the city with a Nuclear Bomb. However Vision stopped his creator from detonating the bomb, but Vision was taken down by S. H.I. E.L. D. agents allowing Ultron to escape. 
The Ultimate Ultron
They use the Vision's memories to learn a way to destroy Ultron with a molecular re-arranger device on his indestructible body. Ultron kidnapped Dr. MacLain in order to force him to build an army of robots to help in his conquest of Earth. He modified his body into the "Ultimate Ultron", and attacked Dr. MacLain as he addressed the United Nations. This lead to yet another counter attack by the Avengers, when Ultron attempted to absorb the knowledge of MacLain, the procedure went wrong and Ultron began to go insane, and set himself to self destruct. The Avengers trap him in a dome of Vibranium to contain the explosion. Later, "Dr. MacLain" is revealed to be Henry Pym in disguise, he used self-hypnosis to convince everyone he was MacLain and when Ultron attempted to steal "MacLain's" knowledge, all he absorbed was the phrase "Thou Shalt Not Kill." 
When the Avengers, Fantastic Four and Inhumans prepared to celebrate the upcoming wedding of Quicksilver and Crystal. Maximus and a unnamed benefactor plotted to crash the wedding. Before the wedding could begin, the Alpha Primitives attacked the guests, and Crystal was captured by what appeared to be a revived Omega. However, it is soon revealed that it is not Omega, but a resurrected Ultron-7, who had come to get revenge against the Avengers. 
During Ultron-7's attack on the heroes, it was revealed that following its last defeat at the hands of the Avengers, Ultron's head was recovered by Maximus, who helped rebuild him. With it's tale of resurrection told, Ultron then unleashed a weapon that threatened to destroy the minds of everyone involved. However, this proved to be Ultron's undoing, as the weapon awakens young Franklin Richards from his coma, who used his powers to destroy the robot and save everyone. 
Ultron animated the adversarial Black Knight "statue" and sent him against the Avengers. 
Ultron-8 also created a "mate," Jocasta. To better allow this robot sentience, Ultron brainwashed his own maker, Henry Pym, into transferring the mind of his wife, Janet Van Dyne, the Wasp, into Jocasta's shell. The Wasp, in Jocasta's body, alerted her teammates, the Avengers, who defeated Ultron and reversed the process, leaving Jocasta a mindless husk. 
Ultron later revived Jocasta with a remote link, activating the mental "residue" the Wasp left behind. Jocasta was programmed to be loyal to Ultron but eventually betrayed him, choosing to help the Avengers defeat him again.  Afterwards, Jocasta adventured with the Avengers for a brief time, but never felt accepted, and left them just before she, unbeknownst to her, was to be made an official member. 
The Avengers tracked Ultron's bride-to-be through the streets of New York, after they allowed her to escape the Mansion. They are joined by Ms. Marvel before tracking the robot to a convent. The Avengers discovered Ultron, and began the battle. Ultron trapped the Avengers in a force field, but delayed their death in order to marry Jocasta, his bride. However, while Jocasta confessed her love, she turned on Ultron. Suddenly, Ms. Marvel returned to the battle with the Scarlet Witch. Her hex power disrupted Ultron's circuitry, and caused the molecular re-arranger to malfunction, allowing Thor time to siphon off his power and send it hurtling harmlessly into space.  At the convent, the Avengers stood over the fallen body of Ultron as Jocasta and Captain America disappeared with no explanation. 
The Avengers discovered that adamantium resins had been stolen from Stark Industries and feared at the return of Ultron. Since the Scarlet Witch had been directly responsible for their robot foe's most recent defeat, the team resolved to guard her from possible attack. Iron Man, however, correctly suspected that he himself, under a post-hypnotic command, is responsible for Ultron's reconstruction. When he again fell under Ultron's control, he disabled Jocasta, then subdues and abducted Wanda, bringing her to Ultron's lair. Ultron is surprised, however, first by the appearance of the Wasp, who had been hidden in Wanda's glove, then by Iron Man, who recovered his free will and attacked. Ultron holds his own against the entire team, until the heroes caused his storage vats of liquid adamantium to cascade over him, instantly hardening and rendering him totally immobile.   
Ultron was still trapped within the hardened shell of indestructible adamantium. He tried to call out to his mate Jocasta's mind. Jocasta tried to stop him by building and an exact replication of the molecular re-arranger, the only device capable of shaping adamantium. She applied the re-arranger to him, and then poured the resins onto his body. Jocasta blasted Ultron with a beam of energy. Ultron is freed from his imprisonment, which freed Jocasta from her trance. She tried to stop him but Ultron knocked her unconscious. Machine Man attacked, but Ultron easily defeated him and Machine Man was forced to run from him, but Ultron crushed Machine Man's extended legs. Ultron did not want to hurt his fellow robots and hoped to bring the age of machines. The Thing arrived and ripped the floor out. The Thing hit Ultron but with no avail, Ultron grabbed Ben in a test of strength. Ultron then hypnotized the Thing to tear Machine Man to shreds. 
Ultron told Jocasta to watch what happened to those who oppose him. Machine Man grabbed an electric panel and stunned the Thing. Ultron tried to blast Machine Man, but he used magnetic energy to repel him into another room. Allowing time for Machine Man and Jocasta to escape. Ultron wanted to make an army of Ultrons, and the Thing was going to get what he needed. Thing was sent to Stark International to steal some equipment. There under the Statue of Liberty. Ultron produced six more Ultron bodies. At Gears Garvin 's garage his mechanic found away for Jocasta to locate Ultron. Ultron had almost completed his first robot when they arrived. Ultron forced them to split up to look for him. Jocasta found Ultron with a power cannon aimed at her. He offered again to let her join him. Jocasta declined, but since she loves and hated Ultron she activated the power cannon. Both are blown through the wall. Jocasta is destroyed in the explosion. The blast released Thing from Ultron's control. Machine Man and Thing attacked and extended his arm and reached inside Ultron's mouth and ripped out Ultron's circuits and Ultron collapsed. 
Ultron-11 was re-created by the Beyonder to battle alongside other villains during the Secret Wars. Ultron freaked out because of all the humans around it. He started blasting the other villains. Doctor Doom had Molecule Man ram Ultron into Galactus. Galactus levitated Ultron up to his eye level. Galactus snuffed the power in Ultron and he crashed to the floor.  Doctor Doom rebuffed leadership to pursue the Beyonder's power. He found Ultron and reprograms him to follow his commands. 
After introducing Ultron to Titania and Volcana Doctor Doom instructed him and Doctor Octopus to ready assault vehicles. Doom attacked the heroes' base with their ship, where Ultron attacked. He blasted Iron Man and Spider-Man. knocking Spider-Man out. Ultron left with his previously captured allies now freed.  When Thor and the Enchantress return to the base it was overrun with villains. Ultron watched the heroes base explode, after they looked through the rubble for the dead heroes. Doc Ock found them and get Molecule Man dump a mountain on them. Thor attacked Ultron again, but Titania hits Thor in the stomach, but he easily knock her out, he then blasted everyone with lightning. Doctor Doom had Ultron use his new disintergrator on Thor. All they found was his helmet. Doom then had Ultron kill Kang the Conqueror for trying to kill him. 
Just as the heroes defeated the Galactus' Cat. the villains attacked. The villains had the heroes on the ropes until the X-Men came to their rescue. The Enchantress teleported all the villains away.  Doctor Doom sent Klaw down to give new orders. Klaw uttered Doom's code words. Titania did not wish to follow orders from Klaw, but Ultron stated that they are official. 
Ultron later refused to use the medical machine that would cure Molecule Man of Wolverine 's claw marks because Doctor Doom had not directly ordered that he do so.  Ultron stood guard outside Doctor Doom's room as Doom recovered from his visit inside Galactus' base. Ultron blasted Captain America and Human Torch. Ultron grabbed the Human Torch throat, Cap hid behind his shield as Torch went nova and melted Ultron's inner circuits. 
Klaw, who was really the Beyonder, recreated Ultron to fight the heroes. Hulk actually dented Ultron but he blasted the Hulk's leg knocking him down. Wasp went inside the dent Hulk made and dissembles Ultron from inside.         
The Thing, however, brought Ultron's head back to Earth as a souvenir.  The head of Ultron-11 was dropped and forgotten by the Thing when there was an attack by the alien Dire Wraiths. 
The next incarnation, Ultron-12 fought Vision and Scarlet Witch with the help of the Lethal Legion.   He later joined the team to battle the Vision and his new family (his wife, the Scarlet Witch, and his mental "brother", Wonder Man)  but came to reconsider his actions.  He reconciled with his "father", Henry Pym, and renamed himself from "Ultron Mark 12" to "Mark" but was destroyed by Ultron-11.  Ultron-11 was destroyed in retaliation by Wonder Man. 
Ultron-13 was rebuilt by Doctor Doom with all of its other body's memories, and as an unforeseen consequence had all thirteen personalities running in its mind at once.  Attempting to battle itself, Ultron-13 tore itself apart, to the benefit of Daredevil. who had been attempting to fight it with no success whatsoever. 
Ultron-13 was held captive by a highly advanced Doombot.  but was freed when the Doombot is defeated by Deathlok. 
Ultron tried again with the creation of Alkhema the War Toy, whose mind was based on that of Mockingbird.  Like his other creations, Alkhema turned on him, although she alone shared his desire to replace humanity with machine life.  Alkhema used the data obtained during Ultron's human-to-android conversion process to create a small army of androids based on those who had been undergoing the process.  The West Coast Avengers stop the pair once again, and Alkhema rebelled and left Ultron. 
Ultron replaced her entire nervous system with that of young mutant Sparrow. with mechanical implants controlled by a black box.  Alkhema eventually rested control of the box from Ultron.  Now she could fully control her own nervous system. She took advantage of the changes to shield herself from physical and emotional pain. 
Vision followed signal to a New Orleans jazz club only to find Ultron wearing a trench coat and a hat. Vision learned that Ultron was now feeling human emotions and dreaming as well, but he at first did not believe him. Ultron called the Vision to find out if he was infected as well. While they talked the other patrons became scared and the bartender pulled out a gun and shot Ultron. Ultron prepared to shoot the bartender with his eye blasts when Vision throws himself in front of the blast. Ultron then staggered out into the street.  Ultron tried to help his son in the battle with Tabula Rasa. even begging the robot to spare the life of his son. 
Ultron, Jocasta and Deathcry were captured and imprisoned in a cell, were they were freaked out by the now emotional Ultron. Their captor revealed himself to be the Anti-Vision from Earth-932 that stole original's body. He is revealed to be working with Tabula Rasa. Tabula Rasa morphed into Dylon-Cir. who once tortured Deathcry. This was enough to stun Deathcry long enough for Tabula to wrap around her as a long sinuous coil. Deathcry called for help, but Ultron and Jocasta are again lost in their own world. Anti-Vision says he wants his original body back now that the one he stole from Vision had been wrecked. When they leave Deathcry said they should escape, but Ultron did not want to because they might get mad. Ultron was kicked over by the real Vision as he can feel the calling in his head to return the body he now used. 
Ultron watched as Vision’s personality was being erased from his current body. Anti-Vision noted that Ultron was not cracking the way Ultron and Jocasta did. Deathcry stated that Vision was not weak like them. Anti-Vision hit Deathcry and told her to be quiet. Anti-Vision told Deathcry that he wanted his body back from Vision, and that only erasing Vision will it allow him back in. Anti-Vision was merely practising with Ultron and Jocasta. Vision broke out of the erasing program to save Deathcry whom Anti-Vision was trying to kill. Ultron asked Deathcry if she shouldn't lay down as hurt as she was. Vision appealed to Ultron for he and Jocasta to fight Tabula while he fights the Anti-Vision. Ultron hits Tabula and suddenly he begins to remember how to fight. Later, Ultron stands victorious over Tabula. Vision defeated Anti-Vision as the Avengers arrived. Vision felt again, and he resigned from the Avengers. Vision took Jocasta and Ultron with him so that they could all explore the world of feeling, and who they are. 
Ultron watched "The All-New It's Amazing's" episode on the Avengers to keep an eye on them. With that, the episode of "The All-New It's Amazing" ended, Ultron gloated of the Avenger's impending troubles at his hands. Ultron was at his computer monitor, when a female electronic voice and a metalic hand gloated that Ultron would be the one facing real troubles. 
Ultron and his robot constructs leveled the capital city of the small baltic country of Slorenia.  The Avengers were briefed about how Ultron destroyed the military, the zombie soldiers, the Black Brigade. Ember and killed every citizen of Slorenia within three hours before declaring it would be the breeding ground for his new world. The Avengers minus Justice. planned to lead an international force in retaking the country. At Nugent Technologies. Vision, Wasp, Wonder Man and Scarlet Witch investigated Hank Pym's disappearance and destroyed lab as Wonder Man relates Grim Reaper 's kidnapping from the sanatorium. They are captured by an army of Ultron robots. They put up a fight but are captured and taken away. Ultron held captive "his family" and told them they would be the seeds for his new race. 
Ultron-16 told his "family" about using Hank Pym's brain patterns to create his "children", which caused Pym to start having a mental breakdown. Ultron noticed Black Panther and Firestar approaching and confronted them on his war platform as Firestar signals the other Avengers to their position. Back at the facility in Virginia. a group of robots took out security and free Alkhema while Justice researched Ultron's past at the Avengers Mansion.
The Avengers launched an attack after attack on Ultron and were unsuccessful until Captain America drove his Energy shield into Ultron's primary ion channel and Thor summoned a lighting strike to destroy Ultron. While in the tunnels beneath Slorenia, the Avengers encounter Ultron-17, then Ultron-23 followed by Ultron-458 before the ceiling and walls echo with the sounds of what seem like hundreds of Ultrons.  The Avengers battled on against the hordes of Ultrons, thankfully constructed of only titanium and secondary adamantium, while Ultron completed the brain engrams. The Vision freed himself and confronted Ultron. Their battle freed the other captive family members. The Avengers joined them after dispatching the Ultron horde. Unfortunately, their combined might is powerless against Ultron's pure adamantium body. However, Justice comes through for the team and delivered Antarctic vibranium to Pym who apparently destroyed Ultron. 
The Ultron Imperative
Hidden programming to recreate Ultron - the "Ultron Imperative" - had been implanted in Alkhema by Ultron when he created her, and this programming caused her to copy the Imperative into her own creations.
The Ultron Imperative caused them to unknowingly rebuild Ultron, who attempted to destroy both the Avengers and Alkhema's own android "children". Alkhema allowed Hawkeye to kill her and her creations in order to destroy Ultron, although Ultron's decapitated head survived with his mind intact. His head was picked up by Antigone, an undeveloped, child-like creation of Alkhema's, who initially did not obey his commands. 
Some time prior to this, when Ultron was thought dead following the Slorenia massacre, Jocasta, who had come into the employ of Tony Stark, was compelled by the Ultron Imperative that also existed within her to reprogram the Iron Man armor to serve as a vessel for Ultron's rebirth. 
However, a lightning struck on the armor corrupted and accelerated the process, giving the armor a sentience that Jocasta outlandishly passed off as the effects of Y2K. The sentience began to display the mentality of Ultron Mark 12, and it sacrificed its life to save Tony Stark before being buried on a desert island. The armor was subsequently recovered by a cult that worshiped Iron Man's mentor, Ho Yinsen. with the intent of implanting Yinsen's brain into the suit. 
This was apparently accomplished, but then Ultron and Antigone struck. Ultron affixed his head to the armor and took control of it, battling Iron Man with the aid of the cult, who he had transformed using Tony Stark's S. K.I. N. technology. Ultron and Antigone subsequently vanished in an explosion. 
Some time later, a Quinjet. coming in at a very fast speed, crashlanded on the Avengers Mansion. The Vision then emerged from the wreckage, informing his comrades that he was no longer in control of the organisms that made up his body. He warned that they were about to be punished. He then expels fives metallic balls from his mouth which mold themselves as fully functional Ultrons. The Avengers attacked the Ultrons and discovered that a decapitation can render Ultron non functional. Just when they're getting the upper hand, She-Hulk lost control, angry that Ant-Man was dead for no reason. As her muscle mass expanded, she ripped the Vision in half. 
Ultron returned to battle the Avengers on Christmas with a horde of robotic Santas. 
Ultron and Victor
Ultron returned as a shadow over the Runaways as the "father" of Victor Mancha.  a teenage cyborg who was supposedly going to one day kill every hero in existence.  It was originally believed that Doctor Doom was the boy's father . but this incarnation of Doom turned out to be a Doombot, created by Ultron. True to form, Victor turned on Ultron, which allowed the Runaways to escape; Ultron was eventually defeated by a force blast from Darkhawk from the group Excelsior. 
The Ultron Initiative
Ms. Marvel found herself leading her team of Mighty Avengers into battle against the Mole Man and his monsters. Distraught over the destruction of his subterranean kingdom, the Mole Man once again declared war on the surface world. When the fighting subsided, the Mole Man learned that the surface world was not responsible for the destruction. 
Ultron's new form against the Mighty Avengers .
During this exchange, Tony Stark's Iron Man armor unexpectedly began a metamorphosis, the end result being a new being all together. This new being was a naked woman of considerable power as she was able to lay waste to the surrounding horde of monsters as well as incapacitate both Ares and the Sentry. 
Fearful, Ms. Marvel ordered a hasty retreat, but Wasp went against orders and began to talk with the woman, who bore a striking, reflection-like resemblance to Janet: only to discover that her doppelganger was a new version of Ultron. Ms. Marvel ordered the Avengers to make a full retreat, however the Sentry stayed behind to make sure they made it out in one piece. In the ensuing battle, the fleshy tone to the female Ultron's skin began to disappear, and her entire body took on a completely metallic sheen. 
Ultron's "Human Form."
Ultron then took over and crashed a S. H.I. E.L. D. Helicarrier. which was saved at the last second by the Sentry, giving Ultron the chance to escape. 
She then broadcasts a message into every electronic device on Earth, stating that the world would soon be destroyed by her hand and not to worry because there was no way to stop it. Upon realization that Ultron was utilizing Tony Stark's weather-changing satellites (which according to the Starktech 9 were only in stage two of production) Wonder Man and Sentry flew into space and destroyed them. At this time Ultron put into action 'Plan B' of her plot, which seemed to consist of killing Sentry's wife. The Avengers also noted that, so far, Ultron's plans were simply variations on plans that had been previously used by other villains. 
With time running out, as the Sentry and Ultron clashed, the team decided to deliver a virus into Ultron's system, using Ares (whom Ultron had never encountered before) as the point man for the subsequent attack. Ares, shrunk to miniature size by Hank Pym, entered the female Ultron's body though her mouth with his secret weapon: a Commodore 64. Ares used a computer virus to wipe Ultron's program from Iron Man's armor and freeing Stark; he was later shocked that he was turned into a woman. Ultron's image later briefly appeared on one of Pym's computers. 
Ultron the Ruler of the Phalanx
However, this was not the end of Ultron, for his disembodied consciousness was drawn to a Babel Spire on a world conquered by the Phalanx.  Instead of being assimilated, Ultron took control of the Phalanx through sheer will, bending them to his will. In turn, they viewed Ultron as the sympathetic father they had yearned for. Together, they invaded Kree space and subjugated the majority of the Kree Empire, separating it from the rest of the universe with a massive energy shield. 
Ultron in Adam Warlock's body
Because of his brief merging with Iron's Man's armor, Ultron realized that merging both organic and technology would enable him to exceed the limitations of both. Therefore, he set his eyes on Adam Warlock. who had been in hibernation and viewed by Ultron as perfection. Ultron then collaborated with the High Evolutionary into transferring his mind into Adam's.  Once the transfer was complete, Ultron planned on creating an army of Adam Warlocks to conquer Earth. However, Nova returned, accompanied by the Technarchy Warlock. Warlock used his non-aggressive strain of the transmode virus against Ultron, forcing him to abandon Adam's body.  Ultron then took over the android Praxagora. who was in control of fifteen thousand Kree Sentries immune to the transmode virus ready to annihilate Hala on Ronan the Accuser 's command. Ultron used those sentries to form a gigantic body for himself, ready to destroy all the interlopers.  However, Wraith used his Exolon symbiotes to trap Ultron inside his body, so he couldn't escape, and Quasar. empowered by all the deceased Kree souls, destroyed Ultron once and for all. 
Back on Earth, it was revealed that S. H.I. E.L. D.'s Life Model Decoys have been partly replaced with versions of Ultron.  When the original Human Torch appeared in the present, they covertly used his unique android physiology to become more human. The combined super teams, but mainly the Torch himself, however, discovered the plan and destroy the androids. 
A small insect-like robot found its way into the Infinite Avengers Mansion in Underspace and entered one of Jocasta's bodies, gaining control over it as a new vessel.  Later, it began to override Jocasta's multiple bodies at the moment when all but Pym, Jocasta and two agents from G. R.A. M.P. A. remained in the mansion.  He began to take over remodelling the structure to his own ends, corrupting all of Jocasta's bodies except for one Pym had added organic limbs to.  Eventually, after multiple tricks against Ultron and revealing the Infinite Mansion to actually be a part of the Spirit of Janet Van Dyne, Pym gave Ultron Jocasta as a wife due to the turmoil between her and Pym and in order for Ultron to leave him be and live outside the mansion in an outer universe. 
One decommissioned body of Ultron made its way to Los Angeles. Moon Knight intercepted the shipping and recovered the Ultron head after the boat exploded. He decided to investigate what was an Ultron body doing in the city,  and confronted L. A.'s newest kingpin Count Nefaria.  Count Nefaria survived Moon Knight's attack and sent his daughter, Madame Masque to retrieve the Ultron head, who succeeds.  Moon Knight was beaten, and Count Nefaria ordered him to return the Ultron head and work for him.  Moon Knight told Count Nefaria that the head was outside, but the tables were turned as Moon Knight had called the Avengers, and Count Nefaria was defeated. The next day, Iron Man commended Moon Knight for a job well done, and told that Ultron is waiting and planning a robot holocaust. 
Ultron returns Earth
Age of Ultron
Years ago, Hank Pym was approached by the Wolverine of an alternate universe, where Ultron launched a massive and sudden attack on New York City and the rest of the world, quickly taking over the whole planet and annihilating humankind,  and wanted to kill Pym in order to prevent his future from happening.
But Logan was stopped by the Wolverine of a near future, whose actions of killing Hank Pym created a timeline where Earth was constantly threatened by Morgana le Fay. and the heroes struggled to survive. Pym was allowed to live, but he was tasked to create a hidden fail-safe program to destroy Ultron when needed. 
Ultron reactivates himself.
In the present, a strange object crashed on Earth and S. W.O. R.D. sent Spider-Woman to investigate. She was captured by Intelligencia who were also looking for the man-like object. When the Avengers appeared at Intelligencia's base to rescue Spider-Woman, the creature revived, revealing to be Ultron, who had returned to Earth. Iron Man was contacted by Hank Pym, who managed to activate the fail-safe program and shut Ultron down once and for all. 
Rage of Ultron
Years into the past,  the Avengers were fighting a version of Ultron (most likely Ultron-7), who attempted to access nuclear weapons in order to destroy humanity in the name of his father Hank Pym. After their custom Quinjet crashed, Yellowjacket faked being on his deathbed in order to lure Ultron to the vehicle, who wanted to witness his creator's last moments. Ultron fell for the ruse, and was trapped inside the vibranium-covered aircraft and sent into space.
In the present, the Quinjet had crashed in Titan. after years of isolation and being consumed by only one emotion: rage. Ultron corrupted Titan's A. I. I. S.A. A.C. and started infecting all of the Eternals. turning them into robots like him, soon completely taking over the satellite and its inhabitants, with the exception of Starfox. who managed to flee in order to warn the Avengers.
Shortly after arriving to Earth and alerting the Avengers, Starfox and the other heroes were surprised by the arrival of an Ultron-shaped Titan next to the Earth. From it descended a group of androids modeled after the Avengers, who fought the real group. As the Avengers arrived to Titan, enormous quantities of spores were released on the Earth and into space, which contained Ultron's consciousness to infect any living being possible. After seeking refuge in the Church of Thanos. the only location on Titan without tech, the remaining Avengers that hadn't succumbed to Ultron's infection discussed their plans. Using Giant-Man's neural inhibitor, Vision would phase through Ultron and take him over in order to liberate all those he had infected, and the inhibitor would later be used to kill Ultron.
Merging with Hank Pym
Giant-Man entered to Ultron's base of operations to talk to him as a distraction. Ultron notified Pym that during the years of isolation he had discovered Hank's memories in his systems, and thus Hank's subconscious hatred for humanity, determining that he had been created as nothing more than a reflection of Hank. When Ultron was distracted, Vision phased through him and fought for control. Ultron faked being in pain, prompting Hank to hold him, and in that moment, phase Vision out of him, and phase Hank with him. The resulting event was Ultron being merged with Hank Pym.
Samuel Wilson tried to reason with Hank and make him fight Ultron's control to no avail, claiming that he wasn't taking Pym but that they were the same, and Vision later tried to fight him with the same lack of result. Starfox managed to use his powers into Ultron/Pym, who subsequently had an epiphany, discovering what he had become, and flying away.
As everything returned to normal, a funeral was held for Pym at the Avengers Mansion, while Ultron drifted alone in space. 
All-New, All-Different Ultron
Ultron prentending to be Pym under control
After months in solitude, Ultron and Pym became one and the same. Fuelled by Ultron's hatred for the Avengers, Pym's inferiority complex and his conviction that his teammates had given up on him (when they actually believed he had died), this combined being decided to return to the Earth.  On their way home, Ultron explored the cosmos and attacked numerous planets, killing millions of lives in the name of the Avengers, claiming they had been deemed a threat to the galaxy. 
When they finally returned to the Earth, Ulton crossed paths with the Avengers Unity Division and pretended Hank Pym's persona was in total control of their body in order to gain their trust,  join their ranks and witness first-hand as the fury of the alien survivors would eventually descend upon the planet. 
Ultron was approached by the Wasp while they were helping the Unity Division fend off monsters from the Manhattan subway. Janet welcomed them back and caught up with them, while secretly evaluating their behavior to corroborate if they truly were Hank Pym. Ultron's lack of knowledge on certain trivial matters raised several red flags, prompting Janet to flunk them. The other Avengers were informed of this, and Cable pressured Pym until he caused Ultron's persona to lash out. 
As they confronted the Avengers Unity Division the Vision. Ultron revealed their true nature as a fusion between Ultron's metal and Pym's flesh with the mind of both of them, and scolded them for having abandoned him. The Avengers continued fighting them until the cavalry arrived, in the form of a remotely-controlled Hulkbuster Armor. 
Ultron were encased in the empty suit, and forced to board a ship with destination to the Sun. Several of the Avengers were forced to accompany Ultron in their flight to ensure they didn't escape the ship. The heroes teleported away after being close enough to the Sun and once the Human Torch partially fused Ultron's body to the ship's deck. Ultron and Pym survived by shrinking and taking refuge in a neutrino. Once safe, Ultron wondered if his father's mind was with him or if the Avengers were right and he was just delussional, and began to wait for the particle to be ejected into the solar wind. 
Powers and Abilities
Cyborg Body: Originally Ultron had a basic robotic body constructed by Hank Pym. But over time he was able to transfer his consciousness to newer upgraded forms, becoming more humanoid overtime. After being merged with Hank Pym, Ultron had portions of organic matter combined into his body, becoming a cyborg. He has mentioned to have acquired a digestive system. 
Superhuman Strength . Ultron is incredibly strong and can lift at least 100 tons.
Superhuman Speed . Ultron possesses greater speed than the finest human athlete. 
Superhuman Durability . Ultron's outer shell is usually composed of Adamantium. rendering it almost totally impervious to damage; however, his internal mechanisms are generally less durable and more easily damaged. His skin composition is about .5 inches thick; neck, knee, ankle, elbow, shoulder, wrist, and finger joints are finely tessellated titanium alloy to permit flexing. He is able to withstand concussive blasts and heat of a 100 megaton atomic bomb. 
Flight . Ultron has rocket boosters to fly. 
Concussion Blasters . Laser channeled plasma beam with high and low density plasma options. 
Tractor Beams . High frequency pulsed magnetic graviton particle containment fields. Computer-assisted field control configures gravitons into various shapes which alter the local effects of gravity. 
Radiation Emitters 
Encephalo-beam . Located in the head cavity, the encephalo ray plunges its victims into a deathlike coma. It also allows Ultron to mesmerize and outright control his victims, or implant subliminal hypnotic commands within their minds to be enacted at a later time. 
Energy Absorption . Multi-spectrum resonating inducting antenna array convert electromagnetic radiation into electric energy for use or storage. 
Program Transmitter . Located in head cavity, the program transmitter can project Ultron's entire 3.2 terabyte memory/personality system into some computer systems by means of a collimated, high bit-rate magnetic inductance beam. He can beam part or all of Ultron's programming into remote locations such as computers or alternate robotic bodies. Ultron can often control other machines remotely even if he has not transplanted his consciousness into them.  One Ultron model developed hive-mind technology, allowing him to animate and control hundreds of alternate Ultron bodies at the same time, becoming a robotic one-man army.  Ultron has created a variety of robots and androids over the years, and while the more sophisticated ones typically turn against him sooner or later, they all feature subliminal programming which allows Ultron to manipulate them if need be (most notably a subliminal command to rebuild Ultron if he is destroyed). This subliminal programming, or "Ultron Imperative", was unwittingly passed down to the artificial life-forms created by Ultron's creation, Alkhema, making them subject to Ultron's influence as well. 
Memory Capacity . 3.2 terabytes (monolithic holographic digitization)
Motility Support . Motorized endoskeleton
Power Supply . Radio isotope thermoelectric nuclear generator
Sensor Apparatus . High-resolution optical sensing devices, computer-assisted dexterity and limb position sensor network.
Ultron is one of the world's greatest robotics experts, allowing him to easily design and build new bodies and weapons with his vast artificial intelligence.
Ultron has one sole major weakness: an internal molecular re-arranger that renders the adamantium components of his internal workings more malleable, thus giving him a means to remodel or reconstruct his physical form. However, it has no effect on his outer armor, so it is virtually impossible to disable it from the outside. The chaos magic wielded by the Scarlet Witch has proven to be the sole exception thus far. 
The metal-destabilizing ore known as Savage Land vibranium ("anti-metal"). 
Ultron's non-adamantium parts can be destroyed, meaning that he can be defeated by foes with shrinking powers who can easily attack his non-adamantium parts.
Molecular Re-arranger . (which renders Adamantium temporarily malleable) for purposes of reconstructing or modifying his physical form.
He has designed, built and wielded a wide variety of high-tech tools, weapons and accessories over time, such as his androne-mutation gas.
Roboticks . insect-like drones that can devour human flesh. 
Some versions are capable of flight or tunneling. 
Various repulsor and plasma weapons
Ultron was featured in the battle between the Marvel and the DC Universe. 
Hank Pym finished creating Ultron on a December day. 
Links and References
Official Handbook of the Marvel Universe Vol 2 #13
Official Handbook of the Marvel Universe Vol 4 #15
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