Legion is an upcoming TV series inspired from the world of X-Men from the FX Network, Marvel Television and executive producer Noah Hawley (Fargo). It stars Dan Stevens, Rachel Keller, Aubrey Plaza and Jean Smart.
Dan Stevens (The Guest, Downton Abbey) has been cast as David Xavier aka the son of Charles aka Professor X. His character is described as: 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 (Parks and Rec) also joins the main cast as David’s friend Lenny. She’s described as: 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 demeanour.
Finally Jean Smart (Fargo) rounds out the latest casting announcements as Melanie: a nurturing, demanding therapist with a sharp mind and unconventional methods.
For some background on what LEGION is — that’s the hero name for David Xavier. According to the X-Men wikia:
When he was very young, David was among the victims of a terrorist attack, in which he was the only survivor. The trauma of the situation caused David to manifest his mutant powers, incinerating the minds of the terrorists. In the process, he absorbed the mind of the terrorist leader, Jemail Karami, into his own. Being linked to so many others at their time of death, he was rendered catatonic, and remanded to the care of Moira MacTaggert at the Muir Island mutant research facility. The trauma caused David’s personality to splinter, with each of the personalities controlling a different aspect of his psionic power.