The paperboy is a reference to Johnny Gosch, a paperboy from Iowa who was on a route with his dog Gretchen and disappeared. His dog was found later, but Johnny's disappearance remains unsolved to this day.
"I think it's fair to say he's my favorite actor I've worked with," said Scott Derrickson about Ethan Hawke. He recalls trying to convince Hawke to do Sinister (2012) despite the actor's protestations that he didn't really like or watch horror. Hawke had been concerned it would be a dark experience, but Derrickson convinced him that it's actually a lot of fun making horror movies. He had to be convinced once again for this film, but it was because he doesn't really play villains and told Derrickson the script would have to be great for him to sign on. Hawke called back that night after reading it, left a voicemail in the voice of The Grabber, and Derrickson knew he had him hooked.
Executive producer Jason Blum, from the House of Blum, sent Scott Derrickson a black phone in a display case after reading the script and giving the film the green light. Derrickson moved into a new house in 2021 and Blum secretly had a black phone mounted on the wall of the new house's basement. "I was just sitting in my living room and I heard a phone ring in the basement, and I was like oh my God." He discovered that Blum had it set to speed dial his cell phone whenever it was lifted from the cradle.
The Grabber dons several creepy masks throughout the film, each exposing different portions of his face. They were designed by legendary prosthetic makeup artist Tom Savini. Mason Thames said that the first time he saw the mask, coupled with Ethan Hawke's bone-chilling performance, he was terrified.
The Grabber is a clown in the short story, but Hill himself suggested in a post-Stephen King's IT world, they couldn't keep that, and should instead switch him to a magician. Early drafts of the script also described the masks as leather ones with a smile or a frown, but Scott Derrickson knew they'd be the centerpiece of the film's marketing, so he spent a lot of time in designing it.