10 X-Men Fates Worse Than Death
8. Fracturing Your Mind Into A Thousand Pieces
Charles Xavier's son, David Haller, can give himself any power he desires, making him theoretically the most powerful mutant on Earth. Sadly, Haller is unable to control his abilities due to his schizophrenia and Dissociative Identity Disorder. Every time he gives himself a new power, his psyche splits into a new personality. Over the years, he has created over a thousand Alters, each with their own unique mutation.
Legion can feel his personalities constantly wrestling for control over his body. When Xavier learned this, he entered his son's mind to compartmentalise his more insidious Alters into a mental prison. But when Legion's father died, he had a mental breakdown, releasing every one of his identities.
Legion lives in constant fear that one of his Alters will consume the world or irreparably destroy the timeline and so, has convinced himself that he's too dangerous to exist. But because of the unique nature of his mutation, killing himself only ends the life of one of his Alters.