FX's 'Legion' Series: 'Downton Abbey' Dan Stevens Joins Aubrey Plaza In 'X-Men' Spinoff Show

The X-Men spin-off series Legion has finally found its David Haller as well as a few of his new friends. Downton Abbey star Dan Stevens has just been cast as the schizophrenic half-mutant, and he will appear alongside Parks and Recreation actress Aubrey Plaza!

The Hollywood Reporter announced the casting news for the FX series, which will be produced by Fargo showrunner Noah Hawley. Stevens will portray David, who happens to be the son of X-Men's Professor Charles Xavier. In the comic books, David is diagnosed with schizophrenia but he later realizes that his visions are actually part of the powers he has inherited from his father.Then he takes on the name Legion and sets out in search for mutants like himself.

Stevens will be joined by Plaza, who will play David's friend (and possible psych ward buddy) Lenny. The character is described as an "impossible optimist" who has a "rough demeanor" that may have been brought on because of substance abuse. Lenny is an original character that was created solely for the show and does not appear in the Legion comic books.

In addition to Stevens and Plaza, Legion will also star Fargo actress Jean Smart as Melanie, a therapist who has "a sharp mind and unconventional methods." She is expected to deal with David and could be the one person who can help him deal with the voices that he hears.

Dan Stevens, Aubrey Plaza, Jean Smart to Star in FX's 'X-Men' Take 'Legion' https://t.co/Nhfhay1OOB @evilhag pic.twitter.com/UcjPvPdZJT

— Hollywood Reporter (@THR) February 4, 2016

Stevens is best known for his portrayal of Matthew Crawley in the TV drama Downton Abbey, but he has also appeared in numerous films like The Guest, A Walk Among the Tombstones and Night at the Museum: Secret of the Tomb. His latest project is the live action adaptation of the Disney classic Beauty and the Beast, where he will play Prince Adam.

Legion will also star The Mentalist actress Rachel Keller, who will play the female lead and possible love interest to Stevens' David. The pilot is expected to start filming in March.