The novel was inspired by a 1949 case of demonic possession and exorcism that Blatty heard about while he was a student in the class of 1950 at Georgetown University.

In September 2011, the novel was reprinted by HarperCollins to celebrate its 40th anniversary, with slight revisions made by Blatty as well as interior title artwork by Jeremy Caniglia.

In flashback sequences, Regan gives Merrin his fatal heart attack, as well as scenes from the exorcism of a young boy named Kokumo in Africa many years earlier.

Adapted and directed by Blatty from his 1983 novel Legion, the film stars George C. Scott and several cast members (Jason Miller (reprising his Academy Award-nominated role from The Exorcist), Ed Flanders, Scott Wilson and George DiCenzo) from Blatty's previous film The Ninth Configuration.

The story takes place 15 years after the events of The Exorcist and turns a supporting character from the first film (philosophical police detective William F. Kinderman (Scott) into the main protagonist.

He investigates a series of brutal murders in Georgetown that resemble the modus operandi of a serial killer executed about the time of the MacNeil exorcism.

Originally titled Legion, the film was drastically changed after rewrites and re-shoots ordered by the studio Morgan Creek Productions.

[13][14][15] Despite his misgivings about the studio-imposed reshoots, Blatty is proud of the finished version of The Exorcist III, having said: "It's still a superior film.

In 2007, Blatty's wife reported on a fan site that "my husband tells me that it is Morgan Creek's claim that they have lost all the footage, including an alternate opening scene in which Kinderman views the body of Karras in the morgue, right after his fall down the steps".

The plot revolves around the crisis of faith suffered by Father Merrin (Stellan Skarsgård) following the horrific events he witnessed during World War II.

After WWII, Merrin is an archaeologist in Cairo, when he is approached by a collector of antiquities who asks him to come to a British excavation in the Turkana region of Kenya.

The local tribesman hired to dig refuse to enter the building, and there are stories of an epidemic that wiped out an entire village.

However, when Merrin, growing suspicious of these rumors, digs up one of the graves of the supposed victims of this plague, he discovers it is empty.

John Frankenheimer was originally hired as director for the project, but he withdrew before filming started due to health concerns.

He is haunted especially by an incident in a small village in occupied Holland during World War II, where he served as the parish priest.

Near the end of the war, a sadistic Nazi SS commander, in retaliation for the murder of a German trooper, forces Merrin to participate in arbitrary executions in order to save a full village from slaughter.

At first, Merrin resists the idea that supernatural forces are in play but eventually helps them, and the ensuing events result in an encounter with Pazuzu, the same demon referenced in The Exorcist.

[25] In June 2022, Burstyn stated that she had completed production for her part in the film, revealing that principal photography had commenced some time previous.

[33] The premise was described as "a propulsive, serialized psychological thriller following two very different men tackling one family's case of horrifying demonic possession, and confronting the face of true evil".

In 1975, Britain released The Devil Within Her (also called I Don't Want to Be Born) with Joan Collins as an exotic dancer who gives birth to a demon-possessed child.

An episode of The Simpsons titled "Home Sweet Homediddly-Dum-Doodily" features Bart, Lisa, and Maggie getting put under the care of the Flanders family.

In the animated comedy horror series Courage the Cowardly Dog, the episode "The Demon In The Mattress" is a direct spoof of the film, using several plot elements that were lifted straight from The Exorcist.

In the episode, Muriel orders a comfy new mattress, not paying attention to the grotesque deliveryman nor the sinister horse-drawn carriage that had delivered it.

Linda Blair appeared in "The Usual Suspects" as a police detective, with the protagonist Dean Winchester finding her character familiar and expressing a strange desire for pea soup at the episode's conclusion.

Since the original release, myths and rumors still exist that a variety of spider-walk scenes were filmed[69][better source needed] despite Friedkin's insistence that no alternate version was ever shot.

This DVD includes the special feature BBC documentary, The Fear of God: The Making of The Exorcist,[71] highlighting the never-before-seen original non-bloody version of the spider-walk scene.

[73][74] In 2025, a haunted house attraction called Universal Horror Unleashed will feature characters from the film franchise.

[76][77] In September 2015, Morgan Creek Productions was selling its library of films, while retaining remake and sequel rights to key properties, including The Exorcist.

David Gordon Green was slated to serve as director, while work on the scripts for the two additional movies was ongoing.

[81][82] On January 11, 2024, the film was removed from Universal's release calendar when Green departed as director as he focused on his production of Nutcrackers starring Ben Stiller, as well as season four of HBO's The Righteous Gemstones.