Legion (David Charles Haller) is a fictional character appearing in American comic books published by Marvel Comics, typically as a villain or supporting character in stories featuring the X-Men and related characters.

He is the mutant son of Charles Xavier and Gabrielle Haller. Legion takes the role of an antihero who has a severe mental illness, including a form of dissociative identity disorder in which each of his identities exhibits different mutant abilities or powers.

The character made his live-action debut in the television series Legion (2017–19), portrayed by Dan Stevens.