The producers scrambled to find someone to play Lord Asriel. They finally found him a Philip Pullman fanboy.

Of all the roles in James McAvoy‘s character Rolodex, which includes Xavier in the X-Men movies and Bill in this year’s It Chapter Two, the actor is most precious when it comes to Lord Asriel in HBO’s His Dark Materials. “I’m probably even more precious about Asriel than they may want me to be sometimes,” the actor tells EW, speaking of the show’s executive producer Jane Tranter and writer Jack Thorne.

The creators were in a bind. As McAvoy tells it, two actors previously backed out from playing Asriel “at the last minute,” leaving Tranter and Thorne “scrambling” to find a replacement. McAvoy, as it happens, visited the home of Kathleen Crawford, the show’s casting director. They were just casually “waxing lyrically” about the source material, author Philip Pullman’s Dark Materials trilogy.

His Dark Materials is a multiverse-spanning saga that begins with Lyra Belacqua (played by Dafne Keen on the show), an orphan girl living in Oxford in a reality that exists parallel to our own. When Lyra’s explorer uncle Asriel visits to present potentially blasphemous discoveries about a particle called Dust to scholars at Jordan College, the young girl foils an assassination plot against him, marking the first in a series of events propelling her towards the arctic north.

There are so many layers to this story. There are daemons, physical manifestations of human souls that exist outside the body as talking animal companions; the Magisterium, this world’s reigning religious institution that claims an authoritarian hold over the populace; and the journey of a child discovering herself while on an inter-dimensional journey. “I was fanboying,” McAvoy recalls of that meeting with Crawford. “Really just getting in deep as fans.”

His Dark Materials
Credit: HBO

Two weeks later, McAvoy got the call to take over the Asriel role — on the Friday before filming was to begin that Monday, no less. “I was like, ‘Look, I can give you 10 days worth of filming if you can make it work.’ And they made it work,” the Glasgow-born actor says. “I had to go up and do It 2, so they squeezed in 10 days of filming before It 2 and then squeezed in 10 days of filming at the end of It 2.”

Now, after shooting his part in the first two seasons, which shot as close together as possible for logistical reasons, McAvoy “really knows the part inside out” to the point where he drives everyone “slightly nuts.” His words, not ours. Game of Thrones actress Indira Varma first introduced McAvoy to Pullman’s novels during work on 2001’s London theater production of Privates on Parade, and he quickly transformed into a “humungous fan.” It’s why he and the creative team on the series have “a thousand, gazillion” conversations on certain elements of the adaptation.

“The narrative drive you need for a TV show or a movie isn’t the same as the focus and attention that you can pay in a novel,” he muses. “Missing things isn’t necessarily the worst thing, you’ve just got to do it right. If you do change something, if you take something away, you’ve got to show everything else tip-top and spick and span.” Asriel only appears in a few episodes — in the beginning of season 1, which adapts a small portion of Pullman’s Book of Dust prequel novel, and one in the finale — but McAvoy’s biggest conversations were about getting such a high fantasy concept across to viewers so that finale would make sense. “In episode 8,” he explains, “there’s a lot of work to do, and incredibly intellectual and metaphysical conversations that Asriel has with Lyra that the audience needs to understand in order for them to have more than a ‘what the f— is going on in this crazy multifaceted and multilayered multiverse that is His Dark Materials?'”

His Dark Materials
Credit: HBO

One scene he shot, though it’s unknown if it will make the final cut of the season, is an interaction between Asriel and his snow leopard daemon Stelmaria (voiced by Helen McCrory) that he found intriguing. He describes it as a “slightly argumentative nature” between the two characters. “Asriel really won’t let anyone argue with him,” McAvoy points out. “He doesn’t really accept anyone else’s opinion except his own. So, it was quite interesting to have him warring with himself and have her warring with herself. They are still very much allies, he’s not at odds with his own soul in the way that the [younger Asriel] from The Book of Dust is, but there’s a bit of antagonism between the two of them.”

It’s really in season 2, adapting The Subtle Knife, the second installment of Pullman’s trilogy, that McAvoy can deeper explore aspects of Asriel that aren’t laid out in the source material. “His absence is a big original factor for Lyra and it’s important to be mysterious,” McAvoy says. “So, we can explore further but actually you end up demystifying him somewhat. He needs to remain an enigmatic and slightly mercurial figure in Lyra’s view. His personal journey is huge but he’s very static in his movement, he’s very solid in his position up to the very end and then everything changes for him.”

At the time EW spoke with McAvoy in mid August, a few weeks after the show’s presentation at San Diego Comic-Con, this super fan said he still hadn’t met Pullman in person, though he expected to at some point. “I’m not bothered about that. That’s alright,” he says. “I’ve had bad experiences meeting the authors that I’m dramatizing in the past, so if I don’t meet him, I might be okay. I sometimes feel it’s better not to meet your heroes.” That, however, is a story for a different time.

His Dark Materials premieres in the U.S. on HBO Monday, Nov. 4.

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