The Exorcist is a 1973 horror film directed by William Friedkin, adapted by William Peter Blatty from his 1971 novel of the same name. The book, inspired by the 1949 exorcism case of Roland Doe, deals with the demonic possession of a young girl and her mother’s desperate attempts to win back her daughter through an exorcism conducted by two priests.
Authors bio is coming up shortly. 