Legion is an FX series that is connected to the Marvel group X-Men. It centers around a superhero who suffers from mental illness in that his superpowers are controlled by different personalities. Whatever you think of multiple personality disorder, that is an intriguing idea for a mutant superhero. The show is doing really well, so if you've just started watching or are looking for a new show to try out, you'll want to learn something about Legion, like who's in it.
For those who are unfamiliar with the name, Dan Stevens is best-known for his roles as Matthew Crawley on Downton Abbey and the Beast in the live adaptation of Beauty and the Beast. He plays David Haller, the titular character who was diagnosed with schizophrenia at a young age. As a result, Stevens went to great lengths to prepare for the role, ranging from speaking with both doctors and people with mental health issues to remaining in the dark about key details of the character and plot so as to achieve a more genuine sense of confusion about what is going on.
Read about the four actresses who play the characters around Haller on Legion at TVOM.