Everyone’s a badass when watching a horror movie until somewhere in the opening credits the words, “Based on a True Story” come up. Because no matter how cliched or dull a horror movie may seem, thinking about how the events unfolding before you more or less happened in real life will always be jarring and spine-tingling. This list features ten horror movies based on true stories we love here on The Mary Sue. 

The Exorcist (1973)

The 1973 classic horror movie flick remains among the highest-grossing films of all time, but only a few will probably know that this movie based on Peter Blatty’s novel of the same name is based on actual events. Blatty took inspiration from the unofficial diaries kept by priests Father Walter H. Halloran and Rev. William Bowdern, who’d conducted an exorcism on a boy given the pseudonym Roland Doe (although it is widely believed that his real name is actually Ronald Edwin Hunkeler). Much of the movie depicted the same eerie instances that occurred in real life such as Doe’s scratches, shouting, spitting, and cursing. However, it’s worth noting that his head didn’t actually turn 360 degrees, nor was there any showing that he’d ever vomited any green ectoplasm. Roland went on to live a long and normal life. He even became a NASA engineer and contributed to the Apollo space missions of the 1960s.