X the Unknown is a British science fiction horror film made by the Hammer Film Productions company and released in 1956. It stars Dean Jagger and Edward Chapman and was written by Jimmy Sangster. The film was directed by Leslie Norman. The film is significant in that "it firmly established Hammer's transition from B-movie thrillers to out-and-out horror/science fiction" and, with The Quatermass Xperiment (1955) and Quatermass 2 (1957), completes "an important trilogy containing relevant allegorical threads revealing Cold War anxieties and a diminishing national identity resulting from Britain's decrease in status as a world power".