Defeated by Strange, Yandroth fell through dimensions uncounted and gained the knowledge he sought, both in magic and physics, and eventually returned to Earth. In a pessimistic, narcissistic move, he created the Omegatron, and engineered it so that upon Yandroth's death, Omegatron would detonate every nuclear stock pile on Earth, so that the world would not long survive his passing. After a car accident he made no effort to avoid, he was visited by Strange, who he informed of his plans.
(Marvel Feature I#1/Last Defenders#5 (fb) ) - After becoming aware of Omegatron's existence, and gathering up Hulk and Namor to assist him, Dr. Strange went to the lighthouse he knew that Omegatron was housed in. Omegatron saw Dr. Strange's astral form and thanked him for helping to bring about the destruction of the world. He said that he would absorb Hulk and Namor's punches and use the energy to activate the nuclear cataclysm. Omegatron said that when he spoke his creator's name, that would act as the trigger. Before Omegatron could absorb enough energy, Strange put a spell on Omegatron and stopped time around it. Strange made the lighthouse appear inactive so no one would accidentally start Omegatron again.
(Last Defenders#5 (fb) ) - Yandroth had the Recorder's head bring Kyle Richmond (Nighthawk) to the Omegatron, during the formation of the original Defenders. There he had Richmond watch as the original Defenders arrived and blundered through the mission. To prove his power over time, Yandroth had Richmond relive when he hit the man with the car, and Richmond realized it was Yandroth he'd hit. Suddenly back at the Omegatron, Richmond wondered about destiny as Yandroth told Richmond he was destiny's pawn. To further prove his power to Richmond, Yandroth plucked alternate versions of the Squadron Sinister from the timestream by combining the power of the Omegatron with his qantum mastery. Richmond was easily overcome by them until a future incarnation of the Defenders (Krang, Nighthawk, She-Hulk, Son of Satan) appeared to help him.
(Last Defenders#6 (fb) ) - Richmond was shocked to see the bizarre battle take place between these supposedly future heroes and the fake Squadron members. Yandroth, determined that this was the correct Defenders team and that Richmond would be responsible for forming it, then disappeared. Realizing Richmond didn't belong in this era Omegatron sent Richmond back to the future where he set up the destined Defenders team he saw in the past.
(Defenders I#1) - Strange used another time spell like the one he used on Omegatron, weakening the spell he used on the Omegatron. The Omegatron's clock resumed its ticking.
(Defenders I#2) - Omegatron was seen counting down to its nuclear explosion at the rate of one second per month.
(Defenders I#4) - Omegatron's countdown to the nuclear explosion continued.
(Defenders I#5) - Valkyrie and Namorita traced a disappeared Hulk and Namor to the lighthouse Omegatron was in. Omegatron was talking very slowly and said that when he spoke his master's name he would destroy the Earth. He revealed that the spell on him was weakened and that time was no longer frozen for him, just very slow. To occupy Valkyrie and Namorita, Omegatron created five Hulks and five Namors, and only one of each was real. The heroes managed to discover the real ones, but they were under the control of Omegatron. Omegatron absorbed enough vibrations to activate his doomsday weapon, and grew a giant body out of the machinery that contained his head. His control over Namor and Hulk was stopped and before he was able to speak Yandroth's name, Hulk knocked him over, and Valkyrie chopped off his head with the Ebony Blade, effectively destroying him. The Ebony Blade could destroy him since it was magical and physical, and while Omegatron was immune to one or the other, it was not immune to both.
(Defenders I#69 (fb) - BTS) - Jeff Colt visited Point Promontory, where—because Strange's spell was deteriorating once again—he found some of the components of the shattered Omegatron. The robot/computer somehow linked itself to his body.
(Defenders I#69) - Colt began to tap into the power of the Omegatron, increasing his own physical abilities in times of need. The more he used the power, the closer he came to activating the Omegatron doomsday device. The Defenders tried to stop Colt—now calling himself the Anything Man—but this just resulted in an ever increasing power usage, which nearly pushed the device over the top when he confronted the Hulk. Finally, they managed to trap him on an island, and with no imminent threats to himself, Colt's powers faded and the device returned to its nearly inert state. With Colt's permission, Strange severed the connection between him and the Omegatron.