The show, which is a spinoff of Marvel's New Mutants series, follows David Haller (Dan Stevens), the son of Professor Charles Xavier and Gabrielle Haller. Admitted to a psychiatric hospital and diagnosed as a paranoid schizophrenic, Haller slowly realizes that the voices he hears in his head aren't delusions, but an effect of his mutant ability.
In the comic, Haller's dissociative identity disorder allows each different version of himself to control a variety of powers. Haller is often viewed as one of the anti-hero figures within the X-Men universe.
New Mutants ran between 1983 and 1991, before it was dissolved and the characters were reintroduced as a part of X-Force.
Nick Grad, president of original programming for FX, said that following showrunner Noah Hawley's run on the award-winning Fargo, both he and Marvel executive Joseph Loeb were excited to see what he could do with the X-Men universe.
"Just as he did in reimagining Fargo, he is bringing an entirely new aesthetic and sensibility to the enormously popular and richly represented X-Men world," Grad said. "The pilot episode is stunning, driven by incredible performances from Dan Stevens, Aubrey Plaza, Jean Smart, Rachel Keller and the rest of the cast."
Plaza will play David's best friend, Lenny. Despite battling alcohol and substance addictions, Lenny has remained an optimistic and overwhelmingly positive figure in David's life, constantly believing her life could change at any moment.
Smart will play Melanie, and although there's not too much information about her character available right now, Marvel did confirm that she'll play a therapist in the show.
Legion is set to start production this summer in Vancouver, with episodes debuting early next year.