William Peter Blatty

William Peter Blatty is most widely recognized for writing the novel "The Exorcist," which he later adapted into an Academy Award-winning screenplay.

Yes, his novel "The Exorcist" was adapted into a highly influential film, and he also directed the film adaptation of his novel "Legion," which was released as "The Exorcist III."

"Legion" is a direct sequel to "The Exorcist," continuing the story with characters from the first novel, though it explores different themes and mysteries.