Sean Justin Penn (born August 17, 1960) is an American film actor and director, also known for being a political activist. He is a two-time Academy Award winner for his roles in Mystic River and Milk, as well as the recipient of a Golden Globe Award for the former and a Screen Actors Guild Award for the latter.

Penn was born in Los Angeles County, California, the son of Leo Penn, an actor and director, and Eileen Ryan (née Annucci), an actress. He has one living brother, musician Michael Penn. Another brother, actor Chris Penn, died in 2006. His paternal grandparents were Jewish immigrants from Lithuania and Russia, while his mother is a Catholic of Italian and Irish descent. According to Penn's mother, Leo Penn may have had distant Spanish ancestry, as the family's surname was originally "Piñón". Penn was raised in a secular home and is an agnostic.

Penn appeared in a 1974 episode of the Little House on the Prairie television series as a then blond-haired extra when his father, Leo, directed some of the episodes.