Monster is a 2003 American biographical crime drama film written and directed by Patty Jenkins in her feature directorial debut. The film follows serial killer Aileen Wuornos, a street prostitute who murdered seven of her male clients between 1989 and 1990 and was executed in Florida in 2002. It stars Charlize Theron (who also produced) as Wuornos, and Christina Ricci as her semi-fictionalized lover, Selby Wall (based on Wuornos's real-life girlfriend, Tyria Moore).

Monster had its world premiere at the AFI Fest on November 16, 2003. On February 8, 2004, it premiered at the 54th Berlin International Film Festival, where it competed for the Golden Bear, while Theron won the Silver Bear for Best Actress. The film was theatrically released in the United States on December 24, 2003, by Newmarket Films. Monster received positive reviews from critics and achieved box office success, grossing $64.2 million on an $1.5 million budget.

The film received numerous awards and nominations, particularly for Theron's performance, including the Academy Award for Best Actress, the Golden Globe Award for Best Actress in a Drama, the SAG Award for Outstanding Lead Actress, the Critics' Choice Movie Award for Best Actress, the Independent Spirit Award for Best Female Lead, and also the Independent Spirit Award for Best First Feature (Patty Jenkins). Theron's acting has received critical acclaim; film critic Roger Ebert called Theron's role "one of the greatest performances in the history of the cinema". The film was chosen by the American Film Institute as one of the top ten films of 2003.