After seven seasons of playing loyal knight Davos Seaworth on HBO's "Game of Thrones," Liam Cunningham took a phone call from the show's creators, D.B. Weiss and David Benioff, urging the Irish actor to cancel his next planned role and join their new mystery project.

"The guys informed me, 'You're not going with them; you're coming with us,'" Cunningham recalls. "And I said, 'OK!' I hung up with them and called my agent. I didn't even know what their project was."

More Davos Seaworth loyalty? Sure. But also a no-brainer as the new series turned out to be Netflix's "3 Body Problem," the long-anticipated Next Big Thing from Weiss and Benioff, who created one of TV's biggest hits with "Thrones."

The creative duo, along with fellow executive producer and writer Alexander Woo, unleash the $160 million, eight-part sci-fi epic "3 Body Problem" on the streaming giant March 21.

"3 Body Problem"Barack Obama turned down a series cameo in the best way to 'GOT' creators

There have been false starts for the "Thrones" pair, who had nothing to do with the HBO sequel "House of the Dragon." In 2017, their planned alternate-history timeline drama based on the Civil War, "Confederate," was canceled after an intense online uproar, and they exited a "Star Wars" trilogy in 2019.

"It was a long and difficult process finding the material we wanted to devote long stretches of our professional lives to," says Weiss of the search that intensified while making "Thrones" eighth and final season, which aired in 2019. "Doing a large-scale series wasn't even a memory. It was happening. It was the weight of that decision."

Just before the "Thrones" Season 8 finale premiered, Netflix executive Peter Friedlander presented the duo with Chinese science-fiction author Liu Cixin's 2008 novel "The Three-Body Problem," whose rabid fan base includes "Thrones" nut Barack Obama (who turned down a cameo in the new series).

After the success of "Thrones," based on George R.R. Martin's novels, Benioff and Weiss instantly knew they would ride the heavy sci-fi – and entirely dragon-free – series, based primarily on Cixin's novel and the author's "Remembrance of Earth's Past" trilogy.

"In a weird way, these books made us feel the same way as the 'Thrones' books," says Weiss. "It was something we hadn't seen on TV before. There was this exhilaration adapting these books for the screen, and terror at the difficulties involved. That combination made it feel just right."

What is '3 Body Problem' about?

The terror started with writing scripts from what many believed was an unadaptable novel, steeped in metaphysics, philosophy and shifting narratives.

"Our first months working together was just talking strategy. How were we going to make this thing into a television series?" says Woo, a producer on HBO's "True Blood." "The main conclusion was the focus on characters that viewers care about and the fact that they care about each other."

"3 Body Problem" revolves around The Oxford 5, a group of brilliant and beautiful former University of Oxford classmates Saul Durand (Jovan Adepo), Auggie Salazar (Eiza González), Jin Cheng (Jess Hong), Will Downing (Alex Sharp) and Jack Rooney ("Thrones" alum John Bradley). The science geniuses are targeted by a highly advanced alien race, the Trisolarians, who are 400 years away from taking over Earth after fleeing their own violently unstable planet. The tight-knit friends reunite and work to repel the invasion with the help of mysterious spymaster Thomas Wade (Cunningham) and his lead investigator Da Shi (Benedict Wong).

"Thrones" fans will hardly recognize Bradley, who played meek Samwell Tarly in that series, as the snarky but loyal snack-empire multimillionaire Rooney in "3 Body Problem."

"We cast John in a role completely different from 'Thrones,'" says Benioff. "His character is based on a conversation we saw John have in a Belfast pub during 'Thrones' where he was very funny, sarcastic and had this caustic wit. John is much closer to Jack Rooney than Samwell."

Along with rewriting most of the characters, "3 Body Problem" also moves the story to England from China. The series starts, like the novel, in 1960s Beijing with the Chinese Cultural Revolution and the violent murder of a scientific intellectual that has repercussions lasting generations.

"After that, it didn't make sense for an English-language show to be set in mainland China," says Benioff. "Just looking at the story and the stakes, it's really about humanity's survival. This is about the world, not about one particular country."

Early on, Cixin gave his blessing for any new direction the English-language TV project would take. (A Chinese-version of the series premiered last year.) "He preemptively told us that he understood large-scale story changes would be made to make it work for television," says Weiss. "That felt good to hear."

The setting will change further, even beyond Earth, in future "3 Body Problem" installments. Successive series haven't been officially greenlit by Netflix, but would be required to complete the trilogy.

"We have plans in our minds mapped out," says Benioff. "There are three books, so there would be at least three seasons. This is a truly global show that gets even bigger than global."

But even the first season of "3 Body Problem" depicts new and visually arresting worlds. Much of the show's spectacle comes as Oxford 5 members Rooney and theoretical physicist Cheng are pulled into an immersive virtual reality game. They experience the perpetual terrors of the alien planet, which is thrown into constant chaos because of the destructive gravitational forces of three star-like suns.

"One of the things that drew us to the books is the spectacle. There are these moments where I can say, 'I've never seen that before,'" says Benioff. "In the year 2024, given all the shows and movies out there, to come across a scene that's just radically different than anything you've seen before – that's pretty wild."