Affleck was born Caleb Casey Affleck 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. As a child he had numerous pets, including cats, snakes, guinea pigs and turtles. Affleck went to George Washington University and later transferred to Columbia University in New York City where he majored in Physics, Astronomy, and Western Philosophy.

Affleck's first movie role was in Gus Van Sant's 1995 dark comedy film To Die For, alongside Joaquin Phoenix and Nicole Kidman as a troubled teenager. 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 Affleck: Chasing Amy and Good Will Hunting. The movie was a major hit and jump-started the careers of Matt Damon and the Affleck brothers. Ben Affleck and Damon went on to win the Academy Award for Best Screenplay. Affleck then starred in the underground movie Desert Blue, a film which met with limited success, but also featured rising star Kate Hudson. He took time off from acting before playing another role.

He next starred in the black comedy Drowning Mona with Bette Midler, Jamie Lee Curtis, Neve Campbell, and Danny DeVito. The movie performed poorly at the box office and with critics. He then starred in the 2001 psychological horror movie Soul Survivors, co-starring Luke Wilson, Wes Bentley, and Eliza Dushku. Affleck later admitted in an interview to Nylon Magazine that he was ashamed to have been involved with both films. However, Affleck followed them up with a re-make of the Rat Pack movie Ocean's Eleven, directed by Steven Soderbergh. The 2001 release had a star-studded cast, including George Clooney, Brad Pitt, Andy Garcia, and Julia Roberts. Affleck played Virgil Malloy, one of the pair of brothers hired to drive the getaway vehicle. Affleck would return to this character in Ocean's Twelve in 2004, and Ocean's Thirteen, released in June 2007, where he has several scenes which take place in Mexico and in which he has extended dialog in Spanish. Affleck lived in Mexico as a child and speaks Spanish fluently.

After establishing his movie career, Casey turned screenwriting and teamed up with Matt Damon to write the 2002 film Gerry about two friends who get lost while hiking in the desert, directed by Van Sant. More recently, Casey starred in the film The Last Kiss as a friend of Zach Braff's character. He also made a cameo in the Joaquin Phoenix-directed video "Tired of Being Sorry" for Balthazar Getty's band Ringside. In 2007 he starred in the Western The Assassination of Jesse James by the Coward Robert Ford, playing Robert Ford to Brad Pitt's Jesse James. This role brought him critical acclaim and also a Golden Globe nomination and Oscar nomination for Best Supporting Actor. Also in 2007 he starred in the critically acclaimed Gone Baby Gone in which he appeared as the main protagonist, Patrick Kenzie. The movie was directed by his brother Ben Affleck.

--Wikipedia