Dan Stevens, Aubrey Plaza and Jean Smart to star on FX's Legion

Dan Stevens, Aubrey Plaza and Jean Smart are to star on FX's Legion. They will join the already announced Rachel Keller on the show.

The pilot episode will follow David Haller, a man who could be more than human and who has had to deal with mental illness since his teenage years. Having been diagnosed as schizophrenic, he has been in and out of psychiatric hospitals for many years. Following a strange encounter with a fellow patient, he is confronted with the possibility that the voices he hears and the visions he sees could actually be real. In the comics, David is the son of X-Men founder Charles Xavier and Gabrielle Haller. The character first appeared in New Mutants No. 25 back in March 1985.

Former Downton Abbey star Dan Stevens will play the role of David Haller with Aubrey Plaza playing Lenny, who is David's friend.

Jean Smart will play Melanie a demanding therapist who has a sharp mind and uses unconventional methods.