Brian Medwin Trenchard-Smith (born 1946) is an English-Australian filmmaker and author, known for his idiosyncratic and satirical low-budget genre films. His filmography covers action, science fiction, martial arts, dystopian fiction, comedy, war, family, thriller, romance and erotica, and his works tend to be cross-genre pieces. After gaining experience as a writer and editor of film trailers, Trenchard-Smith made documentary films for Australian television, many of which focused on stunt performers and martial artists, including his frequent collaborator Grant Page. He made his directorial debut with The Man from Hong Kong (1975), the first film to be produced as an international co-production between Australia and Hong Kong. Many of Trenchard-Smith's films over the next decade became notable examples of the Ozploitation cycle, including Deathcheaters (1976), Stunt Rock (1978), Turkey Shoot (1982), BMX Bandits (1983), Frog Dreaming (1986) and Dead End Drive-In (1986).

Trenchard-Smith moved to Hollywood in 1990, and has since primarily directed made-for-television and direct-to-video films. His other notable works include The Siege of Firebase Gloria (1989), Night of the Demons 2 (1994), Leprechaun 3 (1995), Leprechaun 4: In Space (1996), Happy Face Murders (1999), Britannic (2000), Megiddo: The Omega Code 2 (2001), DC 9/11: Time of Crisis (2003), Aztec Rex (2007), Chemistry (2011), Absolute Deception (2013) and Drive Hard (2014). His debut novel, The Headsman's Daughter (later retitled Alice Through the Multiverse), was self-published in 2016. Several of Trenchard-Smith's films have garnered cult followings and have been subject to critical re-evaluation, and he has also been cited as one of Quentin Tarantino's favourite directors.