Whether it's time travel, clones, alternate futures, or children from said alternate futures, the X-Men are constantly going through events that make their overall story more difficult to understand and recount for others. It's fitting, then, that the poster child for mutants with convoluted backstories is David Haller, AKA Legion, the actual child of Charles Xavier (who, of course, founded the X-Men). Seriously, it can be difficult to pin down verifiable facts about Legion, especially since there's so much stuff we will never see in the TV series.
Legion is now the star of an FX series bearing his name. Yet, the character's relative obscurity has left many wondering, “who is Legion?” The character has a long history of appearances in and around X-Men comics, giving the inclined reader plenty of material with which to familiarize themselves. Despite not being a household name prior to his TV series, Legion has found himself at the center of some truly pivotal moments in X-Men history, and his omega-level powers complicate matters wherever he goes.
He Time Traveled And Killed His Own Father
Legion started out his X-Men career as a quasi-antagonist. Though his intentions were good, his insanity got in the way of him doing the right thing. One such attempt at heroics was his plot to go back in time and kill Magneto, something he believed would help his father achieve peace for mutantkind. This plan backfired horribly when Charles Xavier sacrificed himself to save Magneto, causing Legion to kill him and wreak havoc on the timestream.
Of course, this is doubly sad when you remember that Legion is Xavier's son. While his mother, Gabrielle Haller, was pretty much ordinary, his father was anything but. Charles and Gabrielle had a fling in their younger years, but Xavier had no idea she had gotten pregnant until well after Legion was born.
He Accidentally Caused The Age Of Apocalypse
One of the most famous X-Men story arcs of all time is the Age of Apocalypse, which saw the entirety of the Marvel universe plunged into an alternate reality. This was due to the time-traveling machinations of Legion, who had attempted to go back and kill Magneto, but had accidentally killed his own father instead.
With Charles Xavier out of the picture, the ancient and evil mutant Apocalypse rose to take over the world, leading to a dark timeline full of misery and oppression. The sheer awesomeness of the storylines in this alternate reality makes it an enduring fan favorite.
He Was Unborn At One Point, Then Returned
After being informed that he had destroyed the timeline and created a dark future due to his time-traveling shenanigans, Legion was faced with a difficult choice. Fellow time-traveler Bishop had stopped him from murdering his own father in the past, which is about as good a favor as one mutant can do for another.
The Age of Apocalypse had been averted, but this still left Legion as an extremely dangerous threat to all of reality. Faced with this, Legion decided to "unbirth" himself by traveling through time and making his mother miscarry him (which just has to be the worst way to do that). Of course, this being comic books, that didn’t stick.
He Is An Omega-Level Mutant
Legion’s power levels are nearly unprecedented among mutants. Later publications of X-Men comics would reveal that mutant powers could be “tiered” into various levels, and Legion’s powers were classified right at the top, in the Omega ranking.
In fact, the true upper limits of Legion’s abilities has yet to be fully explored. He has, however, been shown to travel through time and alter reality itself. And that’s on top of his already substantial psychic powers. Legion is the go-to example for those who believe that all mutants are a threat that need to be checked.