While the mutant-massacring Sentinels and Magneto, the Master of Magnetism himself, are more recognizable X-Men villains simply because of how long they’ve been part of the mythos, there’s perhaps no greater threat to the X-Men than the immortal conqueror En Sabah Nur, aka Apocalypse. The X-Men represent the possibility of cooperation and mutual compassion with humankind, and Magneto represents the unmitigated superiority of mutants, but Apocalypse’s entire ethos runs counter to both — only the strong survive. If that means mutants, all the better, but if not, he will waste no tears.
Despite debuting in 1986, 23 years after the X-Men themselves, Apocalypse has become one of Marvel Comics' biggest villains, and the sheer number of times he’s shown up outside the source material is proof. While he’s technically only been the antagonist of one live-action film, 2016’s X-Men: Apocalypse, he’s also been in X-Men: The Animated Series and its sequel series, X-Men ‘97, as well as countless video game appearances starting with the 1992 Super NES game Spider-Man and the X-Men in Arcade’s Revenge. Most recently, he was teased near the end of Marvel’s Wolverine, the newest game from Marvel’s Spider-Man developers Insomniac Games, which sets up a version of the First Mutant and his Four Horsemen that seems a little different from the source material.