The character is an ancient, trans-dimensional malevolent entity who preys upon the children (and sometimes adults) of Derry, Maine, roughly every 27 years, using a variety of powers that include the ability of shapeshifting and manipulation of reality.

It arrived on Earth during an asteroid impact and made its home under the land upon which Derry would later be constructed, initially preying on North American tribes.

However, It's true appearance is briefly observed by Bill via the Ritual of Chüd as a mass of swirling destructive orange lights known as "deadlights", which inflict insanity or death on any living being that sees them directly.

It's natural enemy is the "Space Turtle" or "Maturin", another ancient dweller of King's "Macroverse" who, eons ago, created the known universe and possibly others by vomiting them out as the result of a stomachache.

Throughout the novel It, some events are depicted from Pennywise's point of view, describing itself as a "superior" being, with the Turtle as an equal and humans as mere "toys".

It is finally destroyed 27 years later in the second Ritual of Chüd, and an enormous storm damages the downtown part of Derry to symbolize It's death.

[8][9][10] The Atlantic said of the character; "the scariest thing about Pennywise, though, is how he preys on children's deepest fears, manifesting the monsters they're most petrified by (something J. K. Rowling would later emulate with boggarts).

"[11] British scholar Mikita Brottman has also said of the miniseries version of Pennywise; "one of the most frightening of evil clowns to appear on the small screen" and that it "reflects every social and familial horror known to contemporary America".

[17] Several newspaper articles suggested that the character of Pennywise was an influence, which led to King commenting that people should react less hysterically to the sightings and not take his work seriously.