Exorcism
In Catholic practice the person performing the exorcism, known as an exorcist, is an ordained priest. The exorcist recites prayers according to the rubrics of the rite, and may make use of religious materials such as icons and sacramentals. The exorcist invokes God—specifically the Name of Jesus—as well as members of the Church Triumphant and the Archangel Michael to intervene with the exorcism. According to Catholic understanding, several weekly exorcisms over many years are sometimes required to expel a deeply entrenched demon.
The Exorcist (novel)
Recent investigative research by freelance journalist Mark Opsasnick indicates that Blatty's novel was based on an actual 1949 exorcism of a young boy from Cottage City, Maryland, whom Opsasnick refers to using the pseudonyms Robbie Mannheim and Roland Doe. The boy was sent to his relative's home on Roanoke Drive in St. Louis where most of the exorcism took place.