Eric Lensherr was a poor Jewish man living in Europe who, due to his emerging mutant powers, was the only survivor who watched his family and community fall victim to a Nazi slaughter. Distraught, he wandered the world, where he soon met a young Charles Xavier when both were a member of the Peace Corps in Israel. Xavier befriended Lensherr and revealed their mutual mutant identity, but an attack by Xavier’s son, Legion, from the future, began their ideological split that would divide the two for years to come. At another point, in the Balkan nations, Magneto engaged in an affair with a gypsy woman, who would flee to Wundagore Mountain to give birth to the future Quicksilver and Scarlet Witch.

Lensherr took the name Magnus, alias Magneto, and began to militantly champion for mutant supremacy. He collected other mutants to form the Brotherhood of Evil Mutants, (unknowingly recruiting his children, Quicksilver and the Scarlet Witch,) in trying to force his plans of domination on the world, only to be defeated by Xavier’s plans for peace, embodied in his own team, the X-men. The X-men would routinely clash with Magneto, who often acted alone, but at times reformed the Brotherhood and also formed Mutant Force (now, Redeemers) and the Savage Land Mutates. Among his plans of mutant supremacy was to take over a small South American nation, form his own orbiting space station, Asteroid M, and holding a Soviet nuclear submarine hostage, ultimately killing all on board. At one point during this period, he discovered the truth about the Scarlet Witch and Quicksilver, although the two wouldn’t agree to join him again.

During one such encounter with the X-men, Magneto was defeated and scientifically reduced to the state of an infant by geneticist Moira MacTaggart in the hopes that rearing Magneto "properly" would rid his ideals of mutant supremacy. Although he recovered, perhaps Magneto was indeed changed somehow, as later, Charles Xavier, leaving the planet, left Magnus in charge of his "X-mansion" and its students, the X-men and the New Mutants. Magneto tried to lead the X-men, but instead found their ranks diminish in the so-called "Mutant Massacre," found himself on trial by the UN for his crimes against humanity and infiltrating the villainous Hellfire Club in a misguided attempt to subvert their ranks. Soon, the X-men were scattered across the globe, and the New Mutants off-planet, and Magneto left their ranks. He found himself investigating the Savage Land’s wicked queen, Zaladane, who had succeeded in stealing her "sister’s" magnetism’s powers, and later, Magneto’s own. He had teamed up with a recently resurrected Rogue, engaging in a brief romance, and ultimately defeated Zaladane by killing her in cold blood, to the shock and dismay of Rogue.

Magneto resumed his earlier, villainous ways, attempting to subvert the Scarlet Witch again, to be defeated by the Avengers. Not fully recovering to his former power levels, Magneto was "nursed" back to health by a manipulative Fabian Cortez, who, for purposes of his own, found "worshippers" of other mutants, forming the Acolytes of Magneto. Magneto agreed to lead them and formed a new Asteroid M. Cortez’s attempt to control Magneto and his followers failed due to the X-men’s intervention, but Xavier nonetheless decided to shut down Magneto’s mind to end his villainy, placing him in a coma but allowing an opportunity to create the persona Onslaught.

The Acolytes kept Magneto’s comatose body, but were later defeated by Apocalypse, who caused Asteroid M to crash to Earth, leaving the status of Magneto’s body in question. An amnesiac man resembling a youthful Magneto reappeared and soon entered the life of a wandering Rogue, finding themselves joined with the X-men again, and with the romantic feelings between them resurfacing.