Legion is played by Dan Stevens, also known for his role in Beauty and the Beast.
Dan Stevens . He also starred as David in the thriller film The Guest , Sir Lancelot in Night at the Museum : Secret of the Tomb , and as The Beast/Prince in Walt Disney 's live action adaptation of Beauty and the Beast . Legion (Marvel Comics) . Legion stars in his own TV series of the same name where he is portrayed by Dan Stevens . Legion (TV series) . Dan Stevens stars as Haller , a mutant diagnosed with schizophrenia at a young age .