"It: Welcome to Derry" is not only the first Stephen King adaptation where nobody is safe, it's the first to provide a fully realized backstory for Pennywise the clown, and it seems the original creator of this legendary horror villain had pretty much nothing to do with it. Why? Well, because Stephen King never wrote a backstory for the character into his original novel, which as Andy Muschietti, co-creator and director of "Welcome to Derry," explained during a recent interview, was a work of suspense that intentionally kept audiences in the dark about certain things.
Like all good horror stories, "It" works so well because so much of the story remains a mystery. Who is It? What does It want? And how did It come to Derry? None of these questions are fully explained in King's original 1986 novel, which only serves to make the titular entity that much more unknowable and therefore imposing. This is a creature that feeds on fear, and horror itself thrives on fear of the unknown.
So, when Muschietti, director of the 2017 "It" adaptation and its 2019 sequel, "It: Chapter Two," decided to make a show explaining everything mysterious about the evil force and its most infamous corporeal form, Pennywise, King must have hesitated for at least a second. At least, you'd think he would, but it seems the author was mostly hands-off when it came to crafting the newly-created backstory told in "It: Welcome to Derry," allowing Muschietti and co. to create pretty much unimpeded.