Breaking his oath of noninterference, Uatu the Watcher warned the Fantastic Four of the impending threat of Over-Mind (Fantastic Four #113).
The Watcher later described how Grom, champion warrior among the extraterrestrial Eternals, underwent a scientific procedure long ago to gain the mind power of one billion people and become the evil Over-Mind (#115).
Soon after arriving on Earth, Over-Mind telepathically coerced Mr. Fantastic to turn against his teammates before they could formulate a plan to stop Over-Mind's wave of destruction.
Intent on conquering the world himself, Dr. Doom became an unlikely ally to the remaining members of the Fantastic Four. Yet even the psionic-refractor that Dr. Doom invented did little to halt Over-Mind.
A form of deus ex machina occurred with the arrival of the mysterious Stranger. A composite being from the planet Gigantus, whose ancient inhabitants were enemies of the Eternals, the Stranger had power enough to shrink down and imprison Over-Mind within a mote of dust (#116).