In the novel IT, what is the name and appearance that the monster gives itself?

In Stephen King’s novel It, the monster most famously appears as Pennywise, the Dancing Clown. Its clown appearance is a deceptive form used to lure and frighten children.

It is a shapeshifting, predatory entity that can become whatever its victims fear most, including werewolves, mummies, and other terrifying figures. Pennywise is the form it uses most often, especially when preying on children in Derry, Maine. The novel describes the clown with a white face, red hair, a wide painted smile, a silvery costume, orange pom-poms, and large white gloves.

Pennywise is not the creature’s true cosmic form. During the climactic confrontation, the Losers’ Club encounters the Deadlights, a mysterious extradimensional manifestation that can drive people insane. In the physical world, the monster is also represented as a giant spider-like creature, though that is another manifestation rather than the familiar identity named in the question.

A common mix-up is calling the monster simply “the clown.” Pennywise is the name of its signature clown persona; Flagg is a separate Stephen King character, and Blaine the Mono is the sentient train from The Dark Tower series.