Dan Stevens
as David Haller / Legion
Rachel Keller
as Sydney βSydβ Barrett
Aubrey Plaza
as Lenny Busker
Jeremie Harris
as Ptonomy Wallace
Amber Midthunder
as Kerry Loudermilk
Bill Irwin
as Cary Loudermilk
Hamish Linklater
as Clark Debussy
Jean Smart
as Melanie Bird
Navid Negahban
as Amahl Farouk / Shadow King
Luke Roessler
as David Haller (6-8 Years)
Katie Aselton
as Amy Haller
Mackenzie Gray
as The Eye
Lauren Tsai
as Jia-Yi / Switch
Quinton Boisclair
as Devil with the Yellow Eyes
Ellie Araiza
as Philly
Devyn Dalton
as Angry Boy
Stephanie Corneliussen
as Gabrielle
Jemaine Clement
as Oliver Bird
Brad Mann
as Rudy
Nathan Hurd
as The Monk
Harry Lloyd
as Charles Xavier / Professor X
Scott Lawrence
as Dr. Poole
Kirby Morrow
as Benny
David Selby
as Brubaker
David Ferry
as Dr. Kissinger
Tatyana Forrest
as David's Mother
Dario Giordani
as David's Father
Christian Convery
as David (4 Years Old)
Lillian Lim
as The Monk
Eddie Jemison
as The Greek
Daniel Kailin
as Asian Teenager
Stephanie Van Dyck
as Skeletal Fat Lady
Keir O'Donnell
as Daniel
Sebastian Billingsley-Rodriguez
as David (Toddler)
Jason Mantzoukas
as Jerome / Wolf
Sophie Mackenzie Nack
as Sweetie
Margaux Brooke
as Eloise
Matt Hamilton
as Ben
Mike Azevedo
as 'Renal Failure' Alvarez
Ese Atawo
as Day Room Duty Nurse
June B. Wilde
as Science Teacher
Maddie Phillips
as Jr. Prom Date (Crying)
Stephanie Lavigne
as Patient Dancer #7
Camille Mitchell
as Dr. Bates
Jillian Dion
as Irma Whitecloud
Emily Shuttleworth
as Angry Boy
Gabriel Jacob-Cross
as Ptonomy (5 yrs)
Paul Belsito
as The Man Who Hides
Sharlene Royer
as Ptonomy's Mom
Jesse Chongo
as Buster Debusey
Paul Jarrett
as General Stanley
Jennifer Kitchen
as Burt Hart
Ben Dextraze
as Aide
Christopher Collins
as Wall Street Frat Boy
Nathan Blair
as 10 Year Old Boy
Molly Hagan
as Laura Mercer
Seamus Dever
as Don Eichman
Valentina Izumi
as David's wife
Lily Rabe
as Joan Barrett
Pearl Amanda Dickson
as Teen Syd
Violet Hicks
as Young Syd
Audrey Lynn
as 6 Year Old Syd