The Exorcist

"The Exorcist" was based on the 1971 novel of the same name by William Peter Blatty, which was in turn inspired by the exorcism case of Roland Doe, a pseudonym given to the victim by the Catholic Church. 

Most of the details surrounding Doe's alleged possession and exorcisms come from a diary kept by the attending priest, Fr. Raymond Bishop, and from newspaper reports that came from an at the time anonymous source, which was later revealed to be the Doe family's former pastor, the Reverend Luther Miles Schulze. 

Later, Thomas B. Allen wrote a book about the case, "Possessed: The True Story of an Exorcism" (published in 1993), which was based on two sources: Bishop's diary and the testimony of Fr. Walter Halloran, one of the last surviving eyewitnesses of the events and a participant in the second leg of exorcisms.

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