Set up your iconic and often unruly serial killers. March in your undead armies by their hundreds. But honestly, if you want to creep out even the pickiest of horror fans, all you have to do is show them a clown chilling in a storm drain.

Pennywise the Dancing Clown in "It" is truly nightmare fuel, so much so that even his creator, Stephen King, believes that Pennywise will outlive him like a terror that will never die. But there's a lot more to King's iconic monster, which has a strict diet of fear and children. For one thing, he's an ageless being who doesn't age between the first meeting of the Losers Club and their pulsating reunion and 27 years later, when they're still scarred by the trauma of the other world. Their fear of what awaits down in the bowels of their hometown continues to tickle and lead to it taking many shapes and sizes throughout a story that spans nearly three decades.

In addition to the nightmarish red-nosed button-nosed clown, Pennywise appears to Losers as a werewolf, a sick homeless man living under a house, a lonely old woman, and a giant axe-wielding Paul Bunyan. However, the truth behind Derry's best-kept and darkest secret is that while Pennywise may creep up on children in clown form, his true nature is even stranger.

When we first meet Pennywise in King's horror classic, he claims to have blown himself out of a circus and found himself washed up in a storm, where he meets doomed little Georgie Denborough. It's all a front, though; Pennywise may look like a clown, but it doesn't take long for the mask to slip and reveal the monster. The clown is the form in which Pennywise is most often seen as he stalks the streets of Derry and gets inside the heads of Bill and the Losers, and it was Stephen King's carefully chosen villain.

Pennywise came from a passion to write a book that, as King told an audience in Hamburg in 2013 (via YouTube), had "all the monsters in him". Throwing vampires, werewolves and mummies (oh my!) into the mix, it was clear that the author needed something special to hold them all together. “There must be a binding, horrible, nasty, gross creature. Something you don't want to see. It makes you scream just to see it.” From there, King had his light bulb. "So I thought, 'What scares children more than anything else in the world?' And the answer was "clown".

He's not wrong. Besides iterations of Bill Skarsgård and Tim Curry, there are enough scary clowns in horror that we made our own list. But thanks to some extra special tricks, Pennywise stands out from the rest of the circus.

One of Pennywise's many powers is the ability to transform into whatever its victim fears. The clown is not always present, but for the most part it is the creature's disguise. As King has said many times in interviews, clowns are always scary and that's why they became the main form of monster in "It". Talking to Yahoo!the author recalled his aversion to entertainers wearing big shoes. "I mean, if I was a sick kid and I saw a clown coming, all the red lines would come off my gear, because I'd be scared to death!" So children are afraid of clowns."

In both the book and the film, Pennywise/IT toyed with individual members of the Losers Club in various forms. For Ben Hanscom, it's a mummy. For Bill Denborough, it's his dead brother. For germophobe Eddie Kaspbrak, it was a homeless man offering sex (yes, it's in the book). However, Pennywise the clown always appeared in every encounter, until our heroes learned the true history of the beast. Down in the sewers of Derry, the losers are presented with something that readers, and even some of the stars who brought It to life, had trouble with.

By the end of It, the Losers have learned that Pennywise is an ancient evil not even of this world. An alien who landed on Earth in the 16th century from a dimension known as the Macroverse, her method of hunting was put into effect long before our heroes faced him. They eventually track him to his hidden domain deep beneath Derry, where he presents himself as close to his proper form as possible. That was terrible.

In the final act of the book, Pennywise takes on the guise of a giant egg-laying spider and appears as such in both the 1990 miniseries and the more recent big screen adaptation by director Andres Muschietti. The first attempt at live action was a mix of stop-motion and puppetry and was an absolute joy to life, but it was true to the book. However, it didn't sit well with the original Pennywise, Tim Curry, who later said that “was very disappointed with the endingwhen I turned into a rather unconvincing spider.'

Of course, just like the very nature of "Her," fear is in the eye of the beholder, as Curry rightly points out, "I think whatever scares the pants off you when you're a kid is an image that always stays with you." Well, Sure. Well, it's better than a spotlight, isn't it?

After the clown, the lumberjack, and the sewer-dwelling spider, Pennywise's true form is known as Deadlights. Described as orange lights, any person unlucky enough to look at these luminous rays runs the risk of going insane. Used to trap victims by finally revealing his true form, the Deadlights in the book briefly possessed Bill throughout his childhood, though luckily he escaped. In the 2017 adaptation and its sequel, Beverly and Richie suffered the same experience, but were also released from the view. However, no matter which version you see, there's no denying that it's certainly one of them the weaker endings in King's back catalogue.

Years later the Deadlights would return in King's The Dark Tower series when the Red King (thought to be Pennywise) uses the Deadlights to move between levels of the Dark Tower. He even mentions Derry at one point. However, this interweaving of worlds still doesn't make these hellish fairy lights cool. Despite being floating yellow balls that drive people crazy, they don't really hold a candle to the most commonly used form of the creature. Pennywise will always leave losers and horror fans scared of a smiling clown a little too much.