Terrance Quinn, known professionally as Terry O'Quinn, is an American actor. He is best known for his Primetime Emmy Award-winning performance of John Locke on the TV series Lost (2004–2010). In film, he is best known for playing the title role in The Stepfather (1987) and Howard Hughes in The Rocketeer (1991), with roles in other films such as Heaven's Gate (1980), Silver Bullet (1985), Young Guns (1988), Blind Fury (1989), Tombstone (1993), and Primal Fear (1996).

John Locke is a fictional character played by Terry O'Quinn on the ABC television series Lost. He is named after the English philosopher of the same name. In 2007, O'Quinn won the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series for his portrayal of Locke.