Legion, an X-Men pilot coming to FX, has cast Dan Stevens (Downton Abbey) as the male lead. Variety reports FX announced on Thursday that Dan Stevens, Aubrey Plaza, and Jean Smart would be joining the previously cast Rachel Keller in the pilot.

Stevens will play David Haller, also known in the Marvel universe as Legion. Haller is the son of Charles Xavier, aka Professor X, aka the founder of the X-Men. The son of the powerful telepathic mutant has suffered from mental illness since a young age and is a diagnosed schizophrenic. The pilot will follow Haller who has just about given up on life after he has spent way too much time in psychiatric hospitals trying to find his sanity. After a strange encounter with a fellow patient described as the girl of his dreams (or maybe the girl from his dreams?), he faces the possibility that the voices and visions might actually be real.

Plaza (Parks & Recreation) will play Lenny, Haller’s friend who maintains an optimistic outlook on life despite her history of drug and alcohol abuse. She’s a little rough around the edges, but her hope makes her a likable character. Smart (Fargo) has been cast as Melanie, a sharp-minded therapist. Melanie is nurturing yet demanding of her patients and employs unconventional methods, which sounds scary but nothing has been said to indicate whether it’s the good kind of unconventional or the scary kind that involves dungeons and electricity. Keller (Fargo) will play Syd, an independent woman who hides her optimism underneath a hard exterior.

Deadline  reported Keller’s casting in Legion early in January when it was announced she would be the female lead. I guess that makes her the girl of Haller’s dreams?

Legion marks Stevens’ return to television since his role in Downton Abbey. In Downton Abbey, Stevens played Matthew Crawley, a character who quickly won the heart of viewers but then was hastily written out of the show so Stevens could pursue roles in films. To be honest, I’m still not over how Matthew “left” the show.

Fargo creator, Noah Hawley, wrote the pilot and will executive produce alongside Lauren Shuler Donner, Jim Chory, John Cameron, Jeph Leob of Marvel TV, and Bryan Singer and Simon Kinberg of the X-Men feature franchise.

The pilot’s production is scheduled to begin in March.