Demons are a favorite creature for the horror genre. Ancient and eternal, they come in an infinite variety of forms, and most of the time they don't even need an explanation. Their very existence is all the threat you need to drive the story and create the proper amount of fear.

A lot of the time writers will just make up these malignant spirits. They'll spell their co-writer's name backwards, scramble up the names of favored pets, or just pick something that sounds vaguely threatening. But there are some films out there that did their homework. Films where the demons hunting our protagonists are very real, indeed.

Whether these spirits truly haunt the waking world is up for debate, but they didn't come from the mind of some Hollywood script writer. Rather, they were drawn from real-world texts detailing these dangerous entities.

If you like mixing horror with mythology, then make sure you take a moment to check out What Is The Monster in The Ritual?

If you're a fan of horror-themed lists, on the other hand, then you might get a kick out of 5 Famous Slashers (And Their Real-Life Counterparts), as well as 5 The Purge Movies They Should Make Next.

5. 'Fallen'

The title really should have been a giveaway.

If you haven't seen Fallen, you're probably still familiar with its plot. A cop is tracking a serial killer, but as the case goes on he realizes that what he's following is not human. It's a demon, able to move from host to host to continue cutting a bloody swath.

The demon is Azazel, and he's one of the OG entities when it comes to bad spirits in the Old Testament. According to Britannica, all sin is to be ascribed to Azazel, and he's the entire reason for the holy day Yom Kippur. Leviticus also describes the rite of the scapegoat, where one goat was filled with the prayers for god, and the other was given to Azazel. This is one reason he is so strongly associated with goat imagery.

4. 'Hideaway'

Don't feel bad, no one else has seen this either.

Hideaway is a film based on a Dean Koontz book, and if you've read any of his books then you know what to expect. There are little kids who are unusually mature for their age, weirdly affluent protagonists, and a villain that seems really unique and special, but in the end it turns out to be the same old angels and demons.

With one twist, in this case. While the film is all about a man brought back from the brink of death by an experimental medical procedure, and the weird, psychic link it gives him to a serial killer who calls himself Vassago, that is actually a clue for those versed in the Ars Goetia what's actually happening. Because according to this grimoire, Vassago is a prince of hell, and it is said that if you can summon him that he will reveal the location of things lost or hidden (which might be a reference to the film's title), and he can also tell the happenings of the past, and the comings of the future.

Vassago won't be the last Goetic demon to make this list, either, so consider brushing up on the 72 demons of the Ars Goetia with the documentary at Soul:Ask.

3. 'The Exorcist'

This movie is the reason we have so many possession movies, after all.

Perhaps one of the most famous films in the horror genre to-date, The Exorcist set the standard and has spawned an entire sub-genre for filmmakers who want to have big, scary creatures possessing humans, thus allowing them to save money on flashy effects or big costumes. However, while it was utterly unique at the time in its approach and subject matter, it still remains unique in that the demon being exorcised is not just Satan for the 372nd time.

If you're a fan of the series, then you know the demon we encounter is Pazuzu. For those who aren't up on their history, though, Pazuzu was a potent force in Assyrian and Babylonian times. The demon lord of the winds, according to Ancient History Encyclopedia, Pazuzu brought the dry season that led to famine, and brought the storms and locusts of the wet season. He is mentioned in the epic of Gilgamesh, where the big G slays his brother Humbaba. A horrendous amalgamation of man and animal, Pazuzu was so destructive that ancient people would offer him prayers and sacrifice in attempts to divert his wrath.

2. 'The Nun'

And you thought nuns were creepy before.

If you're a fan of The Conjuring series and its spin offs, you've no doubt taken a look at The Nun. Of course this creature is not a ghost, but rather the chosen form of the demon Valak who has its sights on Lorraine Warren, and who is responsible for so much of the misery and suffering inflicted on her and her husband.

Well, the writers used a less conventional spelling, but Valac is another of the demons described in the Ars Goetia. Valac holds the rank of president among the infernal, and he can grant power over snakes and serpents. Valac is also said to have the knowledge of buried and forgotten treasures, which those who summon him can force him to part with. Valac is often depicted as an angelically winged boy riding a two-headed dragon.

Not sure if that's less, or more, frightening than an angry nun.

1. 'Hereditary'

Come on, you saw this coming.

Hereditary is a horror film that shocked audiences into paying attention, breaking many of the established rules of how these stories go, and spinning a tale that drew us in deeper and deeper to the confusing madness. And in the end, with a single prayer, we realize that the force that's been seeking its new host this whole time is the Paimon, one of the kings of hell.

As Den of Geek points out, Paimon is the ninth spirit listed in The Lesser Key of Solomon, and he is one of the most potent spirits in the whole grimoire. In command of 200 legions, Paimon can teach any art or science to the magician who summons him. He can draw back the curtain of reality and show you the clockwork of the universe. He can bind any man or woman to the magician's will, and he gives good familiars that act as guides and tutors.

Is it any wonder there was a multi-generational cult dedicated to making him happy?