The Legend of Sleepy Hollow resurfaces every year around Halloween. Washington Irving's 1820 tale of a headless horseman who terrorizes the real-life village of Sleepy Hollow is considered one of America's first ghost stories—and one of its scariest.

But Irving didn’t invent the idea of a headless rider. Tales of headless horsemen can be traced to the Middle Ages, including stories from the Brothers Grimm and the Dutch and Irish legend of the “Dullahan” or “Gan Ceann,” a Grim Reaper-like rider who carries his head.

Elizabeth Bradley, a historian at Historic Hudson Valley, says a likely source for Irving’s horseman can be found in Sir Walter Scott’s 1796 The Chase, which is a translation of the German poem The Wild Huntsman by Gottfried Bürger and likely based on Norse mythology.

“Irving had just met and become friends with Scott in 1817 so it's very likely he was influenced by his new mentor's work,” she says, “The poem is about a wicked hunter who is doomed to be hunted forever by the devil and the ‘dogs of hell’ as punishment for his crimes.”

According to the New York Historical Society, others believe Irving was inspired by “an actual Hessian soldier who was decapitated by a cannonball during the Battle of White Plains, around Halloween 1776.”

Irving’s story takes place in the New York village of Sleepy Hollow, in Westchester County. In it, lanky newcomer and schoolmaster Ichabod Crane courts Katrina van Tassel, a young heiress who is also being pursued by the Dutchman Brom Bones. After being rebuffed by Katrina at a party at the van Tassel farm where ghost stories are shared, Ichabod is chased by a headless horseman (who may or may not be his rival) who hurls a pumpkin at the man, throwing Ichabod from his horse. The schoolmaster vanishes.

Irving may have drawn inspiration for his story while a teenager in the Tarrytown region. He moved to the area in 1798 to flee a yellow fever outbreak in New York City, according to the New York Historical Society.

He "would have been introduced to local ghost stories and lore at an impressionable age,” Bradley says.“He cleverly weaves together factual locations—the Old Dutch Church and churchyard, ‘Major Andre's Tree,’ some actual family names, including van Tassel and Ichabod Crane—and a little bit of Revolutionary War history with pure imagination and fantasy," Bradley says. "It's a melting pot of a story, and thus totally American.”

Franz Potter, a professor at National University who specializes in Gothic studies, says the headless horseman, as a supernatural entity, represents a past that never dies, but always haunts the living.

“The headless horseman supposedly seeks revenge—and a head—which he thinks was unfairly taken from him,” Potter says. “This injustice demands that he continually search for a substitute. The horseman, like the past, still seeks answers, still seeks retribution, and can't rest. We are haunted by the past which stalks us so that we never forget it.”

As for folklore mixing with history when it comes to the character of Ichabod Crane, The New York Times reports an actual Col. Ichabod B. Crane was a contemporary of Irving who enlisted in the Marines in 1809, serving 45 years. But there’s no evidence that the two ever met, according to the newspaper.

America’s first ghost story, Bradley says, has endured because it accommodates the changing American imagination.

“It inspires people because it reminds them that there are still some American mysteries, some half-truths that may never be fully known—and that's the whole point," she says. "The ‘Legend’ lends itself to any interpretation, and it continues to fascinate and terrify us in the best possible way.”