Based on the Marvel Comics by Chris Claremont and Bill Sienkiewicz, Legion is the story of "David Haller" (Dan Stevens), a man who believed himself to be schizophrenic only to discover that he is the most powerful mutant the world has ever seen. The third and final season of the mind-bending drama from Noah Hawley returns Monday, June 24 at 10 p.m. ET/PT on FX.