Dan Stevens, who starred on Downton Abbey, has won the lead role in FX’s Legion, the first TV pilot set in 20th Century Fox’s X-Men universe.

Legion began development in October and will also star Rachel Keller. Deadline reported today that Aubrey Plaza (Parks and Recreation) and Jean Smart have also joined.

Stevens will star as David Haller, who is the son of Charles Xavier. He has spent his life in and out of psychiatric hospitals, but his life changes when he meets the girl of his dreams. However, he begins to wonder if the visions he sees might be real.

The pilot was written by Fargo’s Noah Hawley (who worked with Keller and Smart on Fargo season two). The executive producers are Hawley, Simon Kinberg, Bryan Singer, Lauren Shuler Donner, Marvel TV’s Jeph Loeb, Jim Chory and John Cameron.

Legion is looking much better than the other X-Men related pilot Fox is developing. Hellfire was set for the main Fox network, but The Hollywood Reporter confirmed in January that all of its writers have bailed on the project to work on 24: Legacy. That means that Hellfire probably isn’t going to go forward during this pilot season.