The Overmind was originally the alien gladiator Grom of the planet Eternus, he was transformed into the embodiment of the collective psychic might of the Eternian race in order to deal with an invasion by vengeful Gigantians. Sent in a capsule into space to learn how to control his powers, the being now known as the Overmind landed eons later on Earth. Following his new imperative to subjugate the universe, the Overmind entered into battle with the Fantastic Four. However, he was defeated by the Stranger, an entity claiming at that time to be the embodiment of the collective might of the Gigantians.
The Stranger reduced him to microscopic size, but the Overmind was restored by Null the Living Darkness, who mistakenly sent him to the Earth of the Squadron Supreme. Once there, the Overmind took control of U.S. President Kyle Richmond, and through him, the entire planet. The combined efforts of the Squadron, the Defenders, and six psychics were able to defeat the Overmind. The six psychics drove out the Overmind's Eternian consciousness, and took his body for their own. The new, weaker, and more benevolent Overmind joined the Defenders for a time, before wiping their memories of his membership and leaving for parts unknown.