Films: Stephen King's It (1990)
Location: Underground/Civilized Area/Cave
Height/Weight: That of an average human (usually).
Summary: The hardest part of growing up...well, one of the hardest parts is facing your deepest dread. It could be anything, but whatever it is...he knows. Who's he? Oh, no one. Just an ancient cosmic being masquerading as a clown that knows exactly what scares you, and loves it.
History: Pennywise has been around since the dawn of time as the physical manifestation of primal fear. He comes out of hiding every 30 years to haunt the town of Derry and kill mostly children, taking the form of a creepy clown while doing so. Of course, if there is one thing Pennywise loves more than anything, it's feeding on the sheer fright he can induce in people. His most recent target is the Losers Club, a gang of misfit children who must overcome their fears and beat the monster clown back.
Notable Kills: Georgie's early arm-tearing demise, as well as that time he whips out the Deadlights.
Final Fate: Pennywise is driven back by the Losers at first, but 30 years later, he comes at them with a vengeance. They finally manage to kill him in his spider form by knocking him over and ripping out his heart.
Powers/Abilities: Shapeshifting, general invulnerability, and manipulation of reality. He also has the Deadlights, which cause anyone unlucky enough to gaze upon them to devolve into insanity.
Weakness: A lack of fear weakens Pennywise, and ripping out his heart will finish him off.
Scariness Factor: 4-Tim Curry's spirited and creepy performance makes Pennywise one of the scariest clowns ever. Sure, he has his moments of total silliness, but that doesn't often take away the fact that he's a Lovecraftian horror who will try and get your kids.
Trivia: -Pennywise from the original Stephen King book has a much more insane story to tell. To give you an idea, his arch-nemesis is a gigantic God turtle named Maturin who accidentally created the universe, one of his forms is Rodan, and...well, let's just say that there's a rather...special scene with the kid Losers that the clown doesn't even partake in.
-Ironically, Tim Curry was suffering from a major fear of clowns at the time of casting, so it was required that there be no mirrors while he had his makeup on.