10 Most Evil X-Men Villains
7. Mastermind
Rather than a mutant with a superhuman memory for trivia, Mastermind had the power to create incredibly realistic illusions. He was a founding member of the Brotherhood of Evil Mutants but wouldn't reach his full potential until he joined the Hellfire Club and played a key role in The Dark Phoenix Saga.
Posing as an aristocrat, Jason Wyngarde seduced Jean Grey and used his illusions to make her believe she was the Black Queen of the Hellfire Club, allowing the rest of the Club to manipulate her into attacking the X-Men.
Not only was this plan super sleazy, but it also backfired horribly. When Jean saw Cyclops seemingly die, her mind snapped and she became the Dark Phoenix, a cosmic force of destruction who blows up planets for fun. She also broke Jason's mind, leaving him in a coma.
The worst part is, it would later turn out that this wasn't even the first world-ending monster that Mastermind had accidentally created. Mastermind was responsible for making the all-powerful superhero Sentry afraid to use his powers by creating the illusion of the Void, Sentry's evil counterpart who appears when he uses his powers. Unfortunately, Sentry is so powerful he actually willed the Void into existence, causing him to become evil and try to destroy the world.
It's probably for the best that Mastermind eventually died of the Legacy Virus.