The Eternians showered Gigantus with immensely powerful nuclear warheads and detonated them, destroying the planet. A huge armada of Gigantians, however, who had learned the ways of war after eons of peace, escaped the world’s destruction and attacked Eternus in retaliation. Unprepared for so devastating an attack, the Eternians fell. Government leaders realized that their race faced total extinction. Desperately, Eternian scientists prepared to transform Grom, the race’s most outstanding physical specimen, into the receptacle of the collective consciousness and mental might of Eternus. As the surviving population of Eternus marched into huge synthesizing chambers scattered across the planet, their organic brains were converted to pure mental energy and projected into Gram.

When the process was complete, and only the scientists who conducted the process were left alive, the capsule containing Gram was launched into space to incubate until the being learned to control the powers of his group mind. Eons passed. Then Grom emerged as the Overmind, a warrior who possessed the collective psionic power of one billion brains and who carried in his memory the subliminal command to subdue the universe.

The Overmind attacked the first inhabited planet he came upon, the Earth, but was defeated by the Fantastic Four with the aid of the enigmatic alien being called the Stranger. The Stranger claimed to be the embodiment of the collective psionic power of all the surviving Gigantians. The Stranger’s psionic abilities proved to be more powerful than those of the Overmind, and he shrunk the Overmind to microscopic stature and exiled him to a mote of dust.

Several years later, a demonic creature called Null the Living Darkness located the Overmind and decided to use him as a pawn in his scheme of conquest. However, when he restored the Eternian to his original power and stature, Null accidentally transported the Overmind to an alternate Earth instead of the one upon which he had met his defeat. This Earth was the home of the Squadron Supreme. The Overmind took over the mind of President Kyle Richmond and, through him and other selected agents, Overmind conquered the Earth. Squadron member Hyperion sent for reinforcements in the persons of the Defenders. A being composed of the psychic union of six of the alternate Earth’s most powerful telepaths neutralized Null and the Overmind. At the battle’s end, the Overmind’s Eternian consciousness was apparently driven out of its body, and the six telepaths, lacking physical bodies, took refuge inside him.

Now possessing a benevolent mind and a small fraction of his former mental might, the Overmind returned with the Defenders to their world. He assisted the Defenders in several exploits, residing in the interim at Doctor Strange’s mansion. He then mysteriously disappeared from their ranks, using his mental powers to blank out their memories of his presence among them. His current whereabouts and activities are unknown.