Pennywise the Dancing Clown

Pennywise the Dancing Clown, also more commonly known as It, is the main antagonist of Stephen King's 1986 coming-of-age horror novel It, as well as its 1990 film adaptation and its 2017 film remake, It Chapter One and its 2019 sequel, It Chapter Two.
Pennywise is a horrific and malevolent cosmic entity that is billions of years old, spawned in the void of the Macroverse, which is also known as the Todash Darkness. An unknown number of centuries or even millenia ago, it came to planet Earth to feed. Pennywise lives in the sewers of Derry, awakening every twenty-seven years to prey on the town's children, feeding on their fears and using the writhing bright orange lights that comprised his own life essence known as "Deadlights", a dangerous and eldritch form of energy (which is used as a dark magical weapon by another monstrous Stephen King villain known as the Crimson King), to make them "float" before killing and devouring them.
This twisted extra-dimensional entity had a form a human could only comprehend as a giant spider, but It would almost always disguise itself as a clown named "Pennywise the Dancing Clown" to attract children so that it could capture and kill them as they were an easier target. Pennywise could also morph into any form it wished, generally based on its victim's fears.
Due to its shapeshifting abilities, the true identity of the creature is never established. It seems to have no real name, gender or identifiable species, thus the creature is only referred to as "It" by it's enemies, although it is part of an obscure race of shapeshifting monsters called by its Gaelic name "Glamours".
Pennywise encounters a group of local Derry children collectively nicknamed the Losers Club in 1956. It attempts to devour them, but they not only survive, but manage to hurt, battle and partially defeat It. The Losers Club grow into adults twenty-seven years later, and return to Derry after forgetting everything to battle It once again and kill It.