•
Dan Stevens as
David Haller / Legion: The
mutant son of
Charles Xavier, David was diagnosed with schizophrenia at a young age and meets the "girl of his dreams" in a psychiatric hospital. The character possesses various
psychic abilities, including
telepathy,
telekinesis and
teleportation. Stevens joined the series because of showrunner Noah Hawley's involvement, and did extensive research on mental health to prepare for the role, talking to both mentally ill persons and doctors. Hawley and the cast kept secrets from Stevens about the character and plot so that he could identify with David's confusion about himself and reality. •
Rachel Keller as Sydney "Syd" Barrett: A young mutant woman who becomes David's girlfriend. Syd's mind trades places with that of anyone she touches, with hers entering their body, and vice versa. Because of her abilities, the character is portrayed as "withdrawn". She is named after
Roger "Syd" Barrett of the rock band
Pink Floyd, whose music was an important influence on showrunner Noah Hawley. •
Aubrey Plaza as Lenore "Lenny" Busker and
Amahl Farouk / Shadow King: David's friend, an "impossible optimist" despite a history of drug and alcohol abuse. The character dies in the first episode, but returns as the main form and persona, out of several, adopted by the powerful mutant Amahl Farouk within David's mind. Farouk later gives Busker a new body to use, created by infusing Amy Haller's body with Busker's DNA. Busker was originally written for a middle-aged man, until Hawley met Plaza and rethought the character. However, Plaza insisted that the character's dialogue not be changed for her, instead choosing to play the character as both male and female, preceding their reveal as the Shadow King. This led to Busker "making crass remarks about women and muttering vintage phrases". •
Bill Irwin as Cary Loudermilk: A mutant
scientist, one of the founders of Summerland and one of Bird's specialists. The character is introduced in the second episode, but Hawley sought to cast Irwin, for his "playful approach to characters", during filming on the pilot, before the character's role had been written. Hawley "had to pitch him the weird, crazy character dynamic and that the show is about memory and identity", and Irwin agreed to join the project. •
Jeremie Harris as Ptonomy Wallace: A former
child prodigy and a mutant, one of Bird's specialists. A "memory artist", Ptonomy "remembers everything, and has the ability to take people back into their own memories". •
Amber Midthunder as Kerry Loudermilk: A mutant who lives inside Cary's body; their mutant power allows them to coexist in one body or to become separate physical persons. Kerry only ages when she is outside Cary, leaving her physically much younger than he is. •
Katie Aselton as Amy Haller (season 1; recurring season 2): David's adoptive older sister, who tries to remain positive despite his history of mental illness. Hawley said that she defined herself as normal "against her brother. She finds herself being looked at as if she might be crazy, as well." •
Jean Smart as Melanie Bird (seasons 1–2; special guest season 3): A demanding psychiatric therapist. Smart joined the series immediately when asked by Hawley, despite knowing nothing about the show and its source material, due to her previous
Emmy-nominated work with him on the second season of
Fargo. •
Navid Negahban as
Amahl Farouk / Shadow King (seasons 2–3): A malevolent presence in David's mind who takes on several different forms. The character, a psychic with similar capabilities to David, was portrayed in a main capacity in the first season by Plaza, while Quinton Boisclair,
Devyn Dalton,
Kirby Morrow and Jemaine Clement have played his alternate forms. •
Jemaine Clement as Oliver Bird (season 2; recurring season 1; special guest season 3): Melanie's mutant husband. He has spent the last 20 years on the
astral plane. •
Hamish Linklater as Clark Debussy / The Interrogator (seasons 2–3; recurring season 1): An "Interrogator" for Division 3. •
Lauren Tsai as Jia-Yi / Switch (season 3): A young mutant with
time-traveling abilities. ==Episodes==