In April 1985, Stephen King told the Washington Post he was working on a massive new novel; a book he had been “obsessed with for years.” “I’ve been working on the rewrite, and I’m surrounded by this huge manuscript,” he said. “Sometimes I think I should just burn it.” He didn’t burn it. Instead, he finished the book, and it hit shelves just over a year later, in September 1986. The book was called It, and it would become King’s masterpiece. Seemingly everything King knew about how to scare people was packed into this massive tome about an ancient, shape-shifting evil being who liked to eat children.

Stephen King has written many books, but if I had to pick three that stand out the most, at least in the public consciousness, they would be The Shining, Pet Sematary, and of course It. While King didn’t invent the idea of ​​the scary clown, he made it incredibly popular, and every scary horror movie clown since It owes something to King’s Pennywise, that evil trickster who can turn into a million different scary things. King’s book is like The Godfather Part II of horror novels, jumping back and forth in time to tell a massive, sprawling story. In the 1980s, a group of adults who can’t remember their childhood are called back to their hometown to fight a supernatural force that’s preying on children. When they return home, the past catches up with them again, and we see this group battling the beast as children in the late 1950s. Full of American nostalgia and bursts of bloodcurdling horror, It is one of King’s finest works, standing the test of time and terrifying generations.

One reason It has survived so long is because it has been adapted into a movie countless times, finding ways to scare people who haven’t even read the book. It was first adapted as a miniseries in 1990. Tim Curry’s take on Pennywise became iconic almost immediately, and it seemed no one would ever be able to step into his clown shoes. But in 2017, a big-screen adaptation of It came out that traumatized people all over again—and Stephen King had a special requirement for this new take on his classic novel.

The 1990 adaptation of It, which aired in two parts, is beloved by King fans, largely because of Tim Curry’s incredible portrayal of Pennywise. But because the miniseries aired on network television (ABC, to be precise), it had to tone down many of King’s themes. King is an R-rated author, and the novel It doesn’t shy away from graphic, gruesome violence (it also contains a pretty infamous sex scene, which I won’t even touch on here, since both adaptations of It wisely omit that moment entirely). “ABC is one of those networks that still has a pretty strict censorship code,” King told Cinefantastique magazine when the miniseries was in development (via Stephen Jones’ book Creepshows).

When Hollywood came calling again in the 2010s to adapt It for the big screen, King saw it as a chance to do things differently and not shy away from the more explicit elements of his book. “My only requirement was that they try to do as much of the novel as possible, which meant an R rating,” King told Vanity Fair. King added that he wanted the big screen adaptation to be “more full throttle.” He continued:

“The first part was pretty faithful to the book and certainly had its heart in the right place, but television is a medium that’s in a hurry and the budget is a bit low… and in the ’80s there were a lot of things you couldn’t do on television. You couldn’t show children in danger on television, and that’s what this is about.”

When It hit theaters in 2017, the film was clearly rated 18+ – the opening scene alone doesn’t shy away from having a child’s arm bloodily ripped off when Pennywise, unforgettably played by Bill Skarsgård, rips it off. It was also a huge box office hit and ushered in a new boom in Stephen King adaptations for cinema and television – a boom that continues to this day, with many new King projects on the horizon.