Let's watch the many minds of Dan Stevens.
Legion is a weird character to adapt. His real name is David Haller, and he's the son of Professor Charles Xavier--whom we all know as the founder and leader of the X-Men. David is a schizophrenic, and a mutant, with the ability to call upon his many personas rattling around in his brain. Each personality has a unique ability which then David can utilize to his advantage.
As I mentioned, he's a interesting character choice to base an entire television series after. The producers at FX are clearly going for broke, though, with this first trailer. (How about that dance number?) In the comics, Legion has the powers of telepathy, flight, super strength, heat absorption, matter animation, time-manipulation, can belch acid gas (a personal favorite), and teleportation to name but a few. How much they can do on a TV budget will remain to be seen until the show debuts in early 2017, but they're not shying away from the bizarre. Dan Stevens (THE GUEST) is headlining, with Aubrey Plaza, Rachel Keller, and Jean Smart co-starring. FX has a good track record going (TERRIERS, ARCHER, JUSTIFIED, THE AMERICANS, etc.), so I'll be onboard at least at the beginning.