"West Wing" star Martin Sheen spoke with Stephen Colbert about his liberal politics and why he adopted a stage name on "The Colbert Report" last night.

Stephen wanted to know why Sheen is such a "lefty liberal": Sheen has been arrested multiple times for activist activity, earning him first place in The Daily Beast's lineup of "Most Arrested Celebrities." Sheen explained he feels an obligation to "be on the line and serve the common good."

Sheen is popularly known for his portrayal of fictional president Josiah Bartlet on "The West Wing"; he also starred alongside Marlon Brando in "Apocalypse Now," among other prominent film and television roles.

Check out the video above for more from Sheen (including a demonstration of the famous Josiah Bartlet jacket-flip from "The West Wing"), plus a clip from his upcoming appearance in "The Amazing Spider-Man."