Age of Apocalypse
The Age of Apocalypse, also known as Earth-295, was an alternate timeline created when the mutant Legion traveled into the past of Earth-616 and accidentally slew his own father, Professor Charles Xavier. With the power of mutants revealed prematurely, Apocalypse chose to strike early, raising a mutant army and eventually conquering North America. The X-Men were led by Magneto in memory of his murdered friend, and acted as a resistance group against Apocalypse's rule; other mutants, mutant groups, and superheroes all took on radically different roles in this universe. Eventually, the timeline was undone thanks to Bishop, one of the few who'd travelled back to try to stop Legion in his first attempt; after surviving to the present day, Bishop travelled back in time again and stabbed Legion with the mutant's own psychic knife. Legion died, seeing what his actions would have caused, and the Age of Apocalypse was undone. Only a few survived that universe's end, including the evil Holocaust, Dark Beast and Sugar Man, as well as the heroic X-Man (who meshed with the M'Kraan Crystal) and Blink.