The Stepfather is a 1987 American psychological horror film directed by Joseph Ruben and starring Terry O'Quinn, Jill Schoelen, and Shelley Hack. O'Quinn stars as an identity-assuming serial killer who marries a widow with a teenage daughter. Having killed his previous family and changed his identity, his murderous tendencies continue after his stepdaughter becomes suspicious of him. The film is loosely based on the life of mass murderer John List, although the plot is more commonly associated with slasher films of the era. The film was written by Donald E. Westlake, from a story by Westlake, Carolyn Lefcourt and Brian Garfield, with an uncredited rewrite by David Loughery.

The film was theatrically released in the United States on January 23, 1987. It grossed $2.5 million at the box office and was well-received by critics. It has since gained a cult following and was followed by two slasher sequels, Stepfather II (1989) and Stepfather III (1992), and a remake, also called The Stepfather, released in 2009.