Witchfinder General (titled onscreen as Matthew Hopkins: Witchfinder General) is a 1968 British period folk horror film directed by Michael Reeves and starring Vincent Price, Ian Ogilvy, Hilary Dwyer, Robert Russell and Rupert Davies. The screenplay, by Reeves and Tom Baker, was based on Ronald Bassett's 1966 novel Witchfinder General. The film is a heavily fictionalised account of the murderous witch-hunting exploits of Matthew Hopkins (Price), a lawyer who falsely claimed to have been appointed as a "Witch Finder Generall" [sic] by Parliament during the English Civil War to root out sorcery and witchcraft. The plot follows Roundhead soldier Richard Marshall (Ogilvy), who relentlessly pursues Hopkins and his assistant John Stearne (Russell) after they prey on his fiancée Sara (Dwyer) and execute her priestly uncle John Lowes (Davies).

Made on a low budget of under £100,000, the film was produced by Tigon British Film Productions. In the United States, where it was distributed by American International Pictures (AIP), Witchfinder General was retitled The Conqueror Worm (titled onscreen as Matthew Hopkins: Conqueror Worm) by AIP to link it with their earlier series of Edgar Allan Poe adaptations directed by Roger Corman and starring Price; because its narrative bears no relation to any of Poe's stories, American prints book-end the film with his poem "The Conqueror Worm" being read through Price's narration.

Witchfinder General eventually became a cult film, a development partially attributable to Reeves's death nine months after its release. Several prominent critics have championed the film, including Tim Lucas, J. Hoberman, Danny Peary, Robin Wood and Derek Malcolm; their praise has highlighted its direction, performances, and musical score by Paul Ferris.