The Conjuring: The Devil Made Me Do It follows the possession of David Glatzel and Arne Cheyenne Johnson, but in the true story that the film is based on, Glatzel was reportedly inhabited by a whopping 42 demons to be precise! The latest chapter in the Conjuring franchise follows another story associated with the real-life exploits of demon-hunting duo Ed and Lorraine Warren. Despite the diverse host of demons and spooky spirits that exists within The Conjuring cinematic universe, the newest addition to the franchise brought the number of David's demons down to one.
The Conjuring 3 is ultimately about the Warrens attempting to prove that Arne Johnson, accused of murdering his landlord, was actually under the influence of demonic spirits. The film kicks off, however, with the Warrens attempting to exorcise a demon out of 8-year-old David Glatzel, played by Julian Hilliard from The Haunting of Hill House and WandaVision. Arne Johnson, the boyfriend of David's sister Debbie Glatzel, gets possessed after inviting David's demon into his own body, an event that reportedly did take place in real life.
Although The Conjuring is based on real events, various aspects of the story are fiction, while other details are changed for the sake of the movie's story. The Occultist and the curse she leaves on the Glatzels isn't a part of the true story, for example, and the antagonist exists mainly as a way to give the Warrens a sort of arch-nemesis. Channeling all the evil energy of 42 demons into a singular force also makes for easier and less confounding storytelling. Those would have been quite a load of demonic characters and names to explain in a movie that's already more complicated in plot than the other Conjuring entries. Besides, the identity of what is possessing David and Arne doesn't matter so much as the Occultist pulling the strings does.
It's also significant to point out that not even the real-life account provides an accurate number of demons or an explanation of their identities. There's an added "devil" cited as a separate from the otherwise 42 demons, and Judy Glatzel, the mother of David and Debbie, eventually raised the number to 43 demons and two devils. The Glatzels reportedly learned this during "lesser exorcisms," as the Warrens called it, which were deliverances performed by local parish priests. However, the bishop of Bridgeport, Connecticut wouldn't authorize an official exorcism.
Director Michael Chaves explained that there was, in fact, a more established demon character inspired by a young David's description in interviews, but that the idea was ultimately cut for the sake of plot clarity. Since the Warrens were following a paranormal mystery on the road instead of a lone haunted house location, suggesting that there were infernal other forces at work besides just the Occultist would have over complicated the procedural. If one demon was enough to confuse audiences, 42 would have been overboard for The Conjuring: The Devil Made Me Do It. After all, the film was more concerned with fleshing out its human threat this time around than any infernal spirits.