Last month, FX's upcoming X-Men TV series Legion added its first cast member, with Fargo star Rachel Keller signing on as the female lead, although her character wasn't identified. Today we have word from Variety that three more cast members have been added, Dan Stevens, Aubrey Plaza and Jean Smart. The project reunites Jean Smart with Rachel Keller and Fargo series creator Noah Hawley.

Dan Stevens is portraying the lead character David Haller. Since he was a teenager, David has struggled with mental illness. Diagnosed as schizophrenic, David has been in and out of psychiatric hospitals for years. But after a strange encounter with a fellow patient, he's confronted with the possibility that the voices he hears and the visions he sees might be real. While Rachel Keller's exact character has not been revealed, she is said to be, "a scrappy, optimistic woman in her 20s." This report reveals that David is about to give up when he meets the "woman of his dreams," who may be Rachel Keller's character.

Aubrey Plaza is playing David's friend Lenny, who is trying to turn her life around despite struggling with addictions to drugs and alcohol. She is described as having "the likeable energy of the impossible optimist," despite her personal demons. Jean Smart is playing a therapist, described as nurturing yet demanding, who has unconventional methods. It isn't clear how many other main characters have yet to be cast in the series.

RELATED: Legion TV Show Is Not Set in X-Men Universe, Will Debut in 2016

Noah Hawley is executive producing Legion alongside Lauren Shuler Donner (X-Men: Days of Future Past, The Wolverine), Bryan Singer (X-Men: Days of Future Past, Superman Returns), Simon Kinberg (X-Men: Days of Future Past, The Martian), Jeph Loeb (Marvel's Agents of S.H.I.E.L.D., Marvel's Daredevil), James Chory (Marvel's Agents of S.H.I.E.L.D., Marvel's Daredevil) and John Cameron (Fargo, The Big Lebowski). Fox is also developing its own X-Men series dubbed Hellfire, which will be created by Evan Katz, Manny Coto, Patrick McKay and JD Payne. Production on Legion is expected to begin in March.

Noah Hawley recently revealed that his show is not exactly set in the X-Men movie universe, but in a "parallel universe," where the US government is first becoming aware of mutants, although the general public still doesn't know they exist. The series creator also said that he doesn't think there will be any crossover between the movies and his show. What do you think about Dan Stevens, Aubrey Plaza and Jean Smart joining Legion?