“Castle Rock” could not have come together without a blessing from Stephen King, the Hulu anthology drama executive producers said at the ATX Television Festival Friday.

“Stephen was sort of, for us, Charlie in ‘Charlie’s Angels.’ He was sort of the crucial figure who loomed from afar,” Sam Shaw said. “Castle Rock is an important town in the Stephen King library, so it was crucial — we needed and wanted to have his blessing.”

A decade ago Shaw and Dustin Thomason kicked around the idea of a show set in a “kind of generic, off-brand Castle Rock,” Shaw continued. Both men are “reformed fiction writers and were fans of Stephen King and fans of the geography in Stephen King’s” universe. They wanted to explore the kinds of people who would stay in a town after experiencing demonic dogs and serial murderers, but they never thought they’d get the rights to his works.

About a year and a half ago, though, Shaw said, they sat down with Bad Robot, which changed everything.

“It was our understanding that we were not the first people to knock on his door and ask for a cup of sugar and to set a show in the town of Castle Rock,” Shaw said. But having Bad Robot’s J.J. Abrams and Warner Bros. proper behind them made it a go.

“He was flexible and gave us great license,” Shaw said of King.

What then became important was focusing on the story itself.

“There was a really interesting way to approach the material, which is to say, ‘What is a town like Castle Rock now?’ Thomason said. Noting that returning to the place that haunted their childhood dreams, the producers wanted to touch on what it looked like in a modern era.

Shaw added that having to “zipper together” King’s mode of storytelling, which often lays out exactly where a story is going with the “mystery box” and plot twist style for which Abrams is famous.

The first season has one story that will “run its course throughout the episodes” in the “seasonal anthology” style, Shaw pointed out. The idea is that he town is kind of an “advent calendar” and the show can “honor the diversity of the kinds of stories Stephen King tells.” Therefore, both producers like the idea of being able to jump around in time and bringing in different characters that “intersect in different ways.”

The first season, though, will focus on the town as a place that has been “visited and revisited,” featuring some characters are from the Stephen King universe, and some that just share DNA-style traits with previous Stephen King characters.

“Part of what’s great about Stephen King can get lost when you’re trying to ruthlessly cut it down,” Thomason said. Having 10 episodes to explore the story will allow them to dive as deep into character development as King does in his 1000-page novels. And it all starts with with Henry Deaver, played by Andre Holland, who Thomason called “our way into the story.”

Henry is a man who is called to the town and uncovers a mystery there.

“On a genre show, you end up with some characters that end up they’re in a genre story. What we wanted to do…was find actors who really brought you into a world and made it feel totally true and human and natural, even a strange occurrences began to happen around them,” Thomason said, noting that it starts with Holland.

Other key casting included Sissy Spacek, who Thomason called “sort of the original Stephen King star,” as Henry’s adoptive mother; Bill Skarsgard, who he called “the most recent star” and is a man at the center of the mystery Holland finds; Scott Glenn, who plays Spacek’s character’s boyfriend and is kind of a “lion in winter” to the show; Melanie Lynskey and Allison Tolman, who play sisters (the latter of whom was cast after she Tweeted at Lynskey to congratulate her on booking the show and pointed out they should play sisters, the producers announced); and Terry O’Quinn who plays a man who grew up in Castle Rock and saw many tragedies pass through the town.

And then, of course, there is the town itself.

“Casting the town of Castle Rock was almost the most crucial casting in a way,” Shaw said. “A huge amount of work was location work.”

Ultimately, they settled on Orange, Mass. as their shooting location. It was a town the producers saw in the winter and with its barren trees and gray landscape felt haunted and perfect for the tone. The challenge came because a long-term film crew hadn’t come to the area in decades but also because they were effectively asking to borrow a town and “have it stand in for the worst place on Earth,” Shaw noted.

“Castle Rock” will launch with three episodes available at once July 25, with the following episodes unrolling one at a time, not dissimilar to the spring launch plan for “The Handmaid’s Tale.” While Shaw said this was a decision that was made “above his pay grade,” he feels it is the right way to launch the show because he likes the “IV drip” of television rolling out slowly, especially when it’s darker material.

“There are…horror movies and stories that are uncomfortable because you don’t know what to expect from them,” Shaw said. “There’s something queasy-making and unsettling about entering into scenes and stories and not [being] exactly sure what to be afraid of or what you don’t need to be afraid of. And that’s what Stephen King does.”