Casey Affleck (born August 12, 1975) is an acclaimed Academy Award and Golden Globe nominated American actor. He has acted in films such as Good Will Hunting, Ocean's Thirteen, The Assassination of Jesse James by the Coward Robert Ford, and Gone Baby Gone. He is the younger brother of Ben Affleck.

Affleck was born Caleb Casey Affleck-Boldt in Falmouth, Massachusetts, the son of Chris Ann (née Boldt), a school district employee and teacher, and Timothy Affleck, a drug counselor, social worker, janitor, auto mechanic, bartender, and former actor with the Theater Company of Boston. He is the younger brother of Ben Affleck. As a child he had numerous pets, including cats, snakes, guinea pigs and turtles. Affleck went to The George Washington University, later transferring to Columbia University in New York City, where he majored in physics, astronomy, and Western philosophy.

Affleck's first movie role was as a sociopathic teenager in Gus Van Sant's 1995 dark comedy To Die For, alongside Joaquin Phoenix and Nicole Kidman. After starring the following year in the box office flop Race the Sun (co-starring Halle Berry), he appeared in two films featuring older brother Ben: Chasing Amy and Good Will Hunting. The latter was a major hit and jump-started the careers of Matt Damon and the Affleck brothers. Both Ben and Damon went on to win the Academy Award for Best Original Screenplay. Affleck then starred in the underground movie Desert Blue, a film that met limited critical or commercial success, but also featured rising star Kate Hudson. He took time off from acting before playing another role.