William Peter Blatty The author of ‘The Exorcist,’ William Peter Blatty, passed away at 89-years-old. He died this Thursday from a blood cancer called multiple myeloma. Beatty’s book is the inspiration behind an Oscar-winning film, a horror film franchise, and new Fox television show. His book was about a 12-year-old girl who becomes possessed by a demon. It was published in 1971, and the movie inspire by it made $400 million worldwide. Beatty and his story will not be forgotten.