For writers, inspiration can come from anywhere. Herman Melville got the idea for Moby Dick (1851) from Mocha Dick, a real whale who was regularly attacking ships without provocation; Margaret Mitchell may have taken some cues for the character of Ashley Wilkes in Gone With the Wind (1936) based on her distant cousin—laconic lawman Doc Holliday; F. Scott Fitzgerald needed only to look in the mirror to help him find a character for Tender Is the Night (1934), his semi-autobiographical follow-up to The Great Gatsby (1925).

If authors constantly take from real life to shape their fiction, what sorts of experiences feed classic horror novels? Must an author be stalked, spooked, or otherwise assailed by a paranormal entity in order to produce a story that stands the test of time, or do their terrors come strictly from their imaginations? It’s a little of both. Take a look at some very real influences behind some of the scariest books ever written.

1. A Real Exorcism // The Exorcist

William Peter Blatty’s 1971 novel about a young girl named Regan MacNeil possessed by demonic forces and in desperate need of a Catholic priest’s intervention might be one of the most unsettling stories ever printed. (The 1973 film adaptation is no slouch, either, having prompted some audience members to faint.) According to Blatty, the basic premise was culled from real life. In 1949, a 14-year-old boy in Mount Rainier, Maryland, was exhibiting unusual behavior, including abnormal strength, distorted posture, wounds seemingly made from an invisible pitchfork dragging itself over his body, and obscene words that would protrude on his skin like an allergic reaction. Blatty claimed he had notes belonging to the priests who attended to the child in an attempt to rid him of the unnatural forces controlling him, including that of Reverend William S. Bowdern.

Numerous witnesses were said to be present for these episodes, and the boy eventually recovered from whatever might have been plaguing him. Though Bowdern believed it was demonic in nature, one mental health professional, as well as a physicist who consulted on the case, believed the child was exhibiting bizarre but not inexplicable behavior. Bowdern never spoke of the incident, and worked to keep the boy’s identity concealed, though newspaper accounts still leaked in 1949—one of which Blatty read and remembered. In deference to the boy’s privacy, Blatty changed the protagonist to a 12-year-old girl in his novel. Bowdern offered little personal guidance to Blatty, save for a note he sent the author. “I can assure you of one thing,” he wrote. “The case I was involved with was the real thing. I had no doubts about it then, and I have no doubts about it now.”

2. Romanian Folk Tales // Dracula

Bram Stoker sucked inspiration from everywhere for Dracula.FairytaleDesign/iStock via Getty Images

When Bram Stoker began to imagine the world of his 1897 novel Dracula, it’s widely believed he took inspiration from the violent Romanian prince Vlad the Impaler. But there’s scant evidence he based the character on Vlad. Instead, he seemed preoccupied with The Land Beyond the Forest, a book by Irish author Emily Gerard that detailed Transylvanian folklore. Gerard had spent time in Romania and returned home with a surplus of stories about their local legends, including the concept of a nosferatu, who sucks the blood out of victims. Gerard’s passage read, in part:

“Every person killed by a nosferatu becomes likewise a vampire after death, and will continue to suck the blood of other innocent persons till the spirit has been exorcised by opening the grave of the suspected person, and either driving a stake through the corpse or in very obstinate cases of vampirism it is recommended to cut off the head, and replace it in the coffin with the mouth filled with garlic.”

That wasn’t Stoker’s only inspiration. He also drew from a story he had heard from Her Majesty's Coast Guard about the Dmitri sailing ship that was said to have run aground in Whitby Harbor in 1885 and that had only a handful of surviving crew members; Stoker also heard stories of a large black dog running away from the vessel. This would become the Demeter of the novel, a ship that carried Count Dracula to Transylvania.

Stoker’s original preface for Dracula also insisted the events depicted inside actually took place and that the character of Doctor Jonathan Harker, Dracula’s assistant, and wife Mia were people he knew in real life.

3. The Stanley Hotel // The Shining

Prolific master of horror Stephen King doesn’t appear to need many writing prompts, but an unpleasant stay in a creepy hotel influenced his 1977 horror opus The Shining, which was also made into a 1980 movie directed by Stanley Kubrick. King and his wife, Tabitha, visited the Stanley Hotel in Estes Park, Colorado, in 1974, just before it was due to close for the winter; the Kings were the only guests. The hotel, which had originally opened in 1909, hosted the Kings in room 217, where King apparently soaked in the empty and dreamlike atmosphere. He ate in an empty dining room and had a dream about his son running down the halls, screaming in terror while being chased by a sentient fire hose. When he woke up, King had the “bones” of the book all but done.

Room 217 is said to be haunted by Elisabeth Wilson, a housekeeper who nearly died after an explosion caused by a gas leak in 1911; other spirits allegedly roam the halls. It was all enough to make King conjure up the Overlook Hotel, where writer Jack Torrance slowly goes mad. When King (who was not a fan of Kubrick's film) wrote his own made-for-television adaptation of the book, it was shot at the actual Stanley Hotel.

4. A Volcanic Eruption // Frankenstein

Frankenstein's monster may not have been created if not for a volcanic eruption.shelma1/iStock via Getty Images

Much of the lore surrounding the creation of Mary Shelley’s 1818 novel Frankenstein; or, The Modern Prometheus was that Shelley was just 19 years old when she finished writing it. But considering Shelley’s environment of the time, a stark and ghastly story about a mad scientist driven to create life wasn’t so unusual.

In 1815, Mount Tambora in Indonesia erupted, a massive volcanic catastrophe that blanketed the atmosphere in ash and killed 100,000 people. The consequences of the eruption were so extreme that the following year was known as the Year Without a Summer due to failing crops.

This information was not lost on Shelley, who was also an avid follower of the science of the day, including speculation on the nature of life. As a child, she had attended lectures by chemist Sir Humphry Davy, author of Elements of Chemical Philosophy and someone who speculated on the limits of science to make for a better human. These thoughts would soon coalesce into something groundbreaking.

When Shelley arrived in Switzerland in 1816, she found the weather, mood, and atmosphere to be oppressive. Staying with her boyfriend, Percy Bysshe Shelley, their young daughter, and Shelley’s pregnant stepsister, Claire, Shelley found herself indoors most of the time. Then Lord Byron (the father of Claire's baby-to-be) showed up and challenged the group, which also included Dr. John Polidori, to write a scary story to fit the times. Inspired by the conversations of Percy and Lord Byron, who often mused on the limits of modern medicine, as well as her own interest in science, Shelley was more than up to the task. She began writing Frankenstein, a tale of a scientist who exceeds moral boundaries to create life.

5. The Unknown of Pregnancy // Rosemary’s Baby

Author Ira Levin shocked readers with 1967’s Rosemary’s Baby, a chilling depiction of a first-time mother stuck in an upper-class and oblivious society while she fears something might be very wrong with her child. (A 1968 movie had a similar effect on audiences.) Levin said the idea stemmed from his observation that horror is most effective before the horrible thing in question materializes. Levin then thought the most protracted “before” scenario imaginable was a pregnancy. “Nine whole months of anticipation, with the horror inside the heroine!” he wrote in 2003. Levin toyed with making the “father” an extraterrestrial before settling on—spoiler—the devil.

6. A Genealogical Twist // The Haunting of Hill House

Shirley Jackson had an eerie experience researching 1959's The Haunting of Hill House.DNY59/iStock via Getty Images

The Haunting of Hill House (1959) by Shirley Jackson was one of the first attempts to merge the paranormal with scientific inquiry. In Jackson’s story, a supposedly haunted house is descended upon by four scientists who attempt to apply logic and reason to the supernatural activity. (Naturally, science hasn’t prepared them for what they find.) Jackson got the idea for the novel from an account of several psychic researchers of the 19th century who rented a haunted house in order to study it. But that wasn’t the eerie part: In doing further research, Jackson found a photo of an old home in California that appeared to be dilapidated. She thought it was a great visual cue to draw from and asked her mother, who lived in California, if she might be able to find out more about it. As it turned out, the house in question was built by someone in the family—Jackson’s great-grandfather. After being vacant for years, it was ultimately set on fire.

7. Ed Gein // Psycho

To delve into Psycho (1959) lore is to imagine that author Robert Bloch was intimately familiar with the details surrounding real-life serial killer Ed Gein, a resident of Plainfield, Wisconsin, roughly 50 miles from Bloch, who was in Weyauwega. Gein had been convicted of butchering victims and harvesting their skin so that he could “wear” it, possibly as retribution for an overbearing mother.

While those facts align closely with Norman Bates of Psycho fame, Bloch said that it was only the basic premise—an unassuming serial killer—that fueled Psycho. Bloch was compelled by the idea a man could carry out violent crimes for years without anyone suspecting him.

“It was based on the situation,” Bloch told interviewers Randy and Jean-Marc Lofficier [PDF]. “I didn't know much about Mr. Gein personally at that time. I did know that he lived in a small town of 700 people. I was living about 50 miles away in a small town of 1200 people. I realized that [it was] the kind of situation where if you sneezed on the north side of town, on the south side they said ‘Gesundheit!’ So, all I knew was that a man had committed several murders of a shocking nature in a very small community. He had lived there all his life and nobody ever suspected him. It was that situation which made me think there was a story there. So, I based the novel on the situation. It wasn't until later, after inventing the character of Norman Bates, that I discovered how close he was to the real-life Ed Gein.”

8. A Bad Dog // Cujo

Stephen King had his own Cujo experience.Pablo Piraino/iStock via Getty Images

In Cujo (1981), the terrifying, rabid Saint Bernard of Stephen King’s imagination drew heavily from a real-life encounter he had with a worrisome pet. In 1977, King took his motorcycle in to be repaired at a remote mechanic’s ship in Bridgton, Maine. Out came a Saint Bernard, who seemed poised to attack King before his owner—the mechanic—called him off. “Gonzo never done that before,” the man remarked to King. “I guess he don’t like your face.”

Cujo was adapted into a film in 1983. King later said he barely recalled writing it owing to his substance abuse issues at the time. Gonzo, however, remained a firm memory.

9. Really Awful Things // Flowers in the Attic

The chilling 1979 novel Flowers in the Attic by V.C. Andrews details the story of a brood locked away and housebound in order for their grandmother to arrange an inheritance; incest is a key plot point. Clearly, the premise is not for everyone. The Washington Post called it “deranged swill.” But according to Andrews, it wasn’t wholly fictional. Her editor, Ann Patty, said that Andrews told her the story was true based in part on things told to her by one of her physicians, who had a similar experience. “I’d guess that some aspects of it were true,” Patty said. “At least the aspect of kids being hidden away. Whether the twins were real, the sex, the time frame, probably not. I think it was just the concept of kids hidden in the attic so the mother could inherit a fortune.”

10. A Movie With a Twist // The Ruins

The Ruins (2006) was written after author Scott Smith was inspired by director M. Night Shyamalan.stockstudioX/iStock via Getty Images

In The Ruins (2006), author Scott Smith pits his group of protagonists against sentient foliage in Mexico. While Smith had the initial idea back in graduate school of a group of archaeologists who dig up a deadly disease, he decided to pursue it in earnest after seeing director M. Night Shyamalan’s Signs (2002). “I had just seen the movie Signs and thought it would be fun to create that horror movie chill effect,” he said. “When I went back through my folder of ideas and came across this archeologist idea, I thought, what if they dig up something that isn’t a disease but has a horror element instead.”

The Ruins became a movie in 2008. That same year, Shyamalan directed a vengeful plant movie of his own: The Happening.

11. Self-Reflection // American Psycho

When authors admit to their work being partly autobiographical, it’s typically when the protagonist is charming-but-flawed or otherwise somewhat relatable. For Bret Easton Ellis, admitting the misogynistic, preppie murderer Patrick Bateman in 1991’s American Psycho was in some way a reflection of himself was not something he cared to admit. For years, Ellis claimed the character—a Wall Street shark with a fondness for Phil Collins and slaughtering people—was based on his father, who was undergoing a similarly aesthetic metamorphosis in the ‘80s.

In reality, it was more about Ellis’s own struggles with identity and the image he projected to the outside world. “I used [my father] as a scapegoat, in some ways,” Ellis told Rolling Stone in 2016. “The character was much more about me. I didn’t feel comfortable talking about that for a long time because of the outcry over the book and I thought, ‘Oh, God. Why get into that now, since that book [was] so misunderstood?’ So using my father became an easier way to talk about the book. And in some ways, my father had traits similar to Patrick Bateman. I saw him being affected by the new Eighties, male cosmetic overhaul. I was an artist, more liberal than he was, and certainly an outsider in terms of being gay. He was popular, white, privileged, Republican—all these things that Bateman was that I didn’t necessarily feel like I was. I was more interested in the metaphor and how it connected to me.” (Minus, one assumes, all the butchering.)