The men behind adapting the popular "Expanse" novels to the screen faced a massive challenge in Season 2 — finding the perfect actor to play a beloved favorite.

In the first scene of “The Expanse” Season 2, a tough-as-nails soldier in full battle armor charges across the dry Martian landscape, dodging explosions and raining down hellfire. It’s our first glimpse of Bobbie Draper, a bold new addition to Syfy’s complex sci-fi drama — who was also a make-or-break casting problem that the producers were concerned they wouldn’t be able to solve.

In fact, at the beginning of their search, “we dreaded the task of going out into the world and finding this person,” executive producer Hawk Ostly said.

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“The Expanse,” set 200 years in the future, is a grounded and fascinating take on what might really happen to mankind as it spreads across the solar system, based on the book series written by James S.A. Corey (a pen name for authors Daniel Abraham and Ty Franck). The fan favorite character of Bobbie, a Marine who dreams of an independent Mars, is first described in Book 2 of the series, “Caliban’s War,” as follows:

“Bobbie was not the right shape to fit into one of the standard suits, and the Marines made her jump through a series of flaming hoops every time she requisitioned a new custom one. At a bit over two meters tall, she was only slightly above average height for a Martian male, but thanks in part to her Polynesian ancestry, she weighed in at over a hundred kilos at one g. None of it was fat, but her muscles seemed to get bigger every time she even walked through a weight room. As a marine, she trained all the time.”

In the process of adaption, things often change from page to screen, and the producers had taken some liberties in the past with the show’s casting. For example, the character of Naomi, played by Dominique Tipper, was very different in the books: “The character in the book conceals her pain, she hides it on the inside,” executive producer Mark Fergus said, “and Dominique is just not that woman — she’s going to say what she thinks.”

“Most times we just went for the actor who understood the soul of the character, rather than the physicality that the book might have put forward,” Fergus added.

However, for Bobbie, they felt very strongly about not just finding someone who embodied the character on the inside, but also on the outside. Executive producer Naren Shankar said that while there might have been executive-level discussions about changing the character to perhaps bring in a better known actor, the idea never came up between him and his fellow producers.

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The key priority for them was finding someone who matched the book’s description to a T: “Someone who is of Polynesian descent or looks Polynesian and six feet tall and can have this strength and then also this vulnerability behind it,” in Ostby’s words.

Beyond the basic fact of wanting to avoid any sort of whitewashing, and finding a female actor who could believably play the type of soldier the role demanded, the producers pointed to the pre-existing fanbase for “The Expanse” as motivation for making sure, as they said repeatedly, they “got it right.”

The producers were so aware of how challenging it would be to cast Bobbie, as well as how big an addition she would be to the story, that they structured the writing of the season to accommodate it. “What we did on a creative level was slowly work [the character] into the season — she’s in [Episodes] 1, 3 and 6 — partially so she could get used to the part and partially so we could get used to writing the character,” Shankar said.

And that gave them extra time to cast Bobbie, who was the last major player to be added to the show this year. “We were prepared to scour the earth to find the right Bobbie,” Fergus said — to the point where they were ready to consider non-actors, such as athletes, should the right person not appear.

Casting directors Robin Cook (based in Canada), Julie Tucker and her team (working out of New York) and New Zealand-based Liz Mullane were all involved in the hunt for Bobbie, but Ostby said that at the beginning of the search, he was pretty sure that “New Zealand would be a very interesting place to look.” In fact, it was Mullane who first brought Frankie Adams to their attention.

The New Zealand-born actor of Samoan heritage had only a few credits to her name, neither of which were genre roles, but she had something that excited the producers — not just acting experience and the height they were looking for, but years of training as a boxer.

According to Fergus, it was book author Ty Franck who first saw Adams’ tape and identified her as the right choice — something he took as a good sign. “It was a huge thrill for us that one of the guys who invented her character just saw right into her eyes and knew it was her almost immediately,” he said.

Adams, reached via phone just before the show’s premiere, said that when she found out she got the part she “screamed in excitement,” as not only was she excited to play a character with her same ethnic background — something that happens very rarely for her — but the character of Bobbie met at least a few of the things she looks for in a role. “Do I agree with the things she does, yes or no? Would I get a crush on this woman, yes or no?”

Her only concern was that while she was the height they were looking for, she didn’t think she was muscular enough for the part — so she immediately began training for what became dubbed “the Bobbie body,” a regime that was “purely strength and conditioning, no cardio.”

As a boxer, funnily enough, Adams also stood out as unique at her gym, paired against men of a similar height and build for sparring because there were no women in her weight class. However, the experience of facing off against men in the ring gave her a new source of inner strength. “It really boosts your confidence, knowing you can defend yourself like that,” she said.

The result is a casting choice that Shankar called “gold,” and well worth the effort they put into finding an actor who fit the part perfectly. “It requires you to work harder and to go to places that haven’t traditionally been on the radar,” he said. “But when you do, you’re always getting rewarded for it.”

“The Expanse” airs Wednesdays at 10 p.m. on Syfy. Check out an exclusive clip from Season 2, Episode 3 below.

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