Back in October, we reported that FX has issued a pilot order for a new X-Men TV series entitled Legion. Fargo creator Noah Hawley is set to write the pilot script for Legion, with the writer confirming shortly after the show was announced that it will stand alone from the massive X-Men movie universe. Today, Deadline reports that the first cast member has signed on, with Fargo actress Rachel Keller set to play the female lead.

Rachel Keller is best known for playing Simone Gerhardt in Season 2 of Fargo. She impressed Noah Hawley and FX executives so much in that show that they gave the actress her first leading role in Legion. The actress has previously appeared in the 2014 indie feature Hollidaysburg, along with guest starring spots on The Mentalist and Supernatural last year.

The Legion pilot episode will introduce the story of David Haller. Since he was a teenager, David has struggled with mental illness. Diagnosed as schizophrenic, David has been in and out of psychiatric hospitals for years. But after a strange encounter with a fellow patient, he's confronted with the possibility that the voices he hears and the visions he sees might be real. Rachel Keller's character is said to be, "a scrappy, optimistic woman in her 20s."

Related: FX's Legion TV Show Will Standalone in X-Men Movie Universe

There are rumors that the female lead's powers may be associated with human touch, which could be similar to X-Men mutants such as Rogue or Spyke. It isn't known if this unspecified character has also been diagnosed as a schizophrenic like David Haller, or how she comes into contact with him. It isn't known when production may begin, or when FX may be eyeing to air this series.

Noah Hawley is executive producing Legion alongside Lauren Shuler Donner (X-Men: Days of Future Past, The Wolverine), Bryan Singer (X-Men: Days of Future Past, Superman Returns), Simon Kinberg (X-Men: Days of Future Past, The Martian), Jeph Loeb (Marvel's Agents of S.H.I.E.L.D., Marvel's Daredevil), James Chory (Marvel's Agents of S.H.I.E.L.D., Marvel's Daredevil) and John Cameron (Fargo, The Big Lebowski). Fox is also developing its own X-Men series dubbed Hellfire, which will be created by Evan Katz, Manny Coto, Patrick McKay and JD Payne. What do you think about the first casting addition for Legion?