Caleb Casey McGuire Affleck-Boldt (born August 12, 1975) is an American actor and director. He began his career as a child actor, appearing in the PBS television film Lemon Sky (1988) and the miniseries The Kennedys of Massachusetts (1990). He later appeared in three Gus Van Sant films – To Die For (1995), Good Will Hunting (1997), and Gerry (2002) – and in Steven Soderbergh's comedy heist trilogy Ocean's Eleven (2001), Ocean's Twelve (2004), and Ocean's Thirteen (2007). His first leading role was in Steve Buscemi's independent comedy-drama Lonesome Jim (2006).

Affleck's breakthrough was in 2007, when he was nominated for the Academy Award for Best Supporting Actor for his performance in the western drama The Assassination of Jesse James by the Coward Robert Ford and acted in the crime drama Gone Baby Gone, directed by his brother Ben Affleck. In 2010, he directed the mockumentary I'm Still Here. He then had a string of successful films in the early 2010s, with Tower Heist, ParaNorman, and Interstellar, and received particular praise for his performance as an outlaw in the indie film Ain't Them Bodies Saints.

In 2016, Affleck starred as the lead in the drama film Manchester by the Sea. For his performance as Lee Chandler, a grief-stricken man, he won the Golden Globe, BAFTA and Academy Award for Best Actor, and received a Screen Actors Guild Award nomination. In 2017, Affleck received critical acclaim for his leading role in the supernatural drama film A Ghost Story.