what is the exorcist based on

"The Exorcist" is based on the real-life exorcism of a young boy from Cottage City, Maryland in 1949, as well as the horrifying 1634 Loudun exorcisms. The novel was inspired by the possession of Roland Doe, a 14-year-old boy who underwent exorcisms at different locations, including his home, Georgetown University Hospital, and The Alexian Brothers Hospital. The author, William Peter Blatty, was inspired to write the novel after reading about Roland Doe while he was a student at Georgetown University. The true story of "The Exorcist" involves a boy referred to as "Roland Doe," whose chilling ordeal became the real-life inspiration for the novel and subsequent film adaptation.