What sort of guide book was founded by Leslie Halliwell?

Robert James Leslie Halliwell (23 February 1929 – 21 January 1989) was a British film critic and encyclopaedist (and television impresario) who in 1965 compiled The Filmgoer's Companion, the first one-volume encyclopaedia devoted to all aspects of the cinema. He followed it a dozen years later with Halliwell's Film Guide, another monumental work of effort and devotion. In an age long before the internet, Halliwell's books were regarded as the number one source for movie information and his name became synonymous with film knowledge and research.