'The Last of Us': Pedro Pascal and Bella Ramsey on Fan Expectations for the Upcoming Series (Exclusive)

'It became very clear, very quickly, how much people loved the game...and that was scary.'

While their characters in The Last of Us have to weather a post-apocalyptic hellscape and cannibalistic attackers, Pedro Pascal and Bella Ramsey are up against something perhaps equally ominous: a devoted legion of video game fans waiting with bated breath to see how the HBO adaptation holds up to their hopes and dreams.

"We're exhausted!" Pascal joked with ET's Ash Crossan about living up to fan expectations with the upcoming series. "It became very clear, very quickly how much people loved the game, and the experience of playing the game, and that was scary."

"This is the next level of really getting into something, by like an immersive experience of playing these characters, and so people's relationship to that experience is a deep one," he continued. "We want to kind of expand on that and meet expectations, surpass expectations, learn something new, show something new, and also honor what is originally there."

The series, based on the hugely popular Naughty Dog video games, centers on Joel (Pascal), a grizzled and traumatized man who is charged with smuggling a 14-year-old girl, Ellie (Ramsey), across the country in the hopes that she may be the key to developing a cure to whatever has mutated part of the population into cannibals.

Ramsey revealed that the pair was "advised, encouraged and ordered" not to play the games before taking on the role, but admitted that they both "did research" on their characters.

"To me it was like immediately exciting to me -- the content of it and the story," Ramsey noted.

For executive producer Craig Mazin -- who co-created the series along with The Last of Us video game creator Neil Druckmann -- part of the concerns over finding the perfect Joel and Ellie for the series came from video game fans' love for Troy Baker and Ashley Johnson, who voiced and provided motion capture for the characters in the game series.

"Pedro was kind of an easy one," Mazin admitted. "He responded to the material immediately, and we had such a great conversation with him. And one of the things that came out right away was that he's- Well, we know he's a tough guy, you know, he can carry himself, he can be dangerous. But there's this vulnerability, there's a soulfulness there that is so important for Joel, because this is a broken man who thinks he's closed off and then he's not."

"Ellie was trickier, because Ellie was portrayed by Ashley Johnson brilliantly in the game," he continued. "Ashley was a woman in her 20s playing a 14-year-old girl, so what you get from the game is this interesting, far more sophisticated 14-year-old than you would imagine."

"We saw over a hundred people and when we saw Bella's audition, and it was, 'That's it, we're done, we got it. [They're] Ellie,'" Mazin recalled. "You know who said it, was Ashley. Ashley was like, 'That's it, [they're] Ellie.' And who else would know better?"

It didn't hurt, of course, that Pascal and Ramsey had something of a connection already. Both starred in fan-favorite roles on Game of Thrones. Though their characters never interacted onscreen, Pascal said it was "an unspoken bond" for the co-stars.

"I watched the show before I got the job, and I continued watching it after I got it, so I got to meet and fall in love with Lyanna Mormont in the way that everyone else did," he recalled. "And Bella was Ellie before I was Joel, and so it was so exciting for me to know that I was gonna be with them on this journey."

When it comes to Last of Us fans being spoiled for the series because they played the video game and know some of the major plot points, Mazin said he's not concerned.

"We have this experience a lot. We don't necessarily recognize when it's happening but we go to see movies or watch television shows that are about things that we already know about," the producer noted. "Like Chernobyl, it blew up, the Titanic sank, we still go to the movies because it's the relationships that carry us through."

"Our exploration of the relationships in the show, I think, had a chance to be deeper and richer, because we have more time to spend on the story," he continued. "And people who know the game well are going to see and feel a lot of new things... I would say this one is about the journey. Just like Joel and Ellie go on a journey, the audience goes on a journey, and that's the experience that matters more than anything else."

And while the nine-episode first season of the series covers the entirety of the first Last of Us game, there are plenty more stories to tell within the canon. The 2013 game was followed by a sequel, The Last of Us Part II, in 2020, and other storylines have also been explored in the games' downloadable content. Mazin said he would love the chance to "dive into more of the world of The Last of Us" in future seasons.

"We have definitely talked about seasons to come," he revealed. "I think everybody at HBO is excited about keeping it going, we want to keep it going. So as long as the audience is there and the desire's there for more, we're ready to go."

The Last of Us premieres Jan. 15 on HBO and HBO Max.