Dan Stevens, Aubrey Plaza, and Jean Smart join FX’s Legion FX has announced today that Dan Stevens (The Guest), Aubrey Plaza (“Parks and Rec”) and Jean Smart (“Fargo”) have joined the cast of their new pilot, a spin-off of the popular X-Men franchise. Stevens will play the role of David, the son of Charles Xavier, who is described as folllows: “Diagnosed as schizophrenic at a young age, David is a haunted man, trying to find his way back to sanity, but he’s getting tired and is about to give up when he meets the girl of his dreams.: Aubrey Plaza joins as Lenny, David’s friend, who despite a life of drugs and alcohol abuse, knows that any day now her life is gonna turn around, which gives Lenny the likeable energy of the impossible optimist despite her rough demeanor.