"We found an actress in New Zealand named Frankie Adams who has been a local star in NZ for a while and is also an amateur female boxer," Franck told entertainment news site blastr.com. "She's six feet tall, she's athletic, she can act, and she's Samoan.
"Bobbie is very physical so we wanted an actress who was very comfortable with being physical. An actress who never appeared to be intimidated in any situation but who could occupy as much space as any of the other cast and could be intimidating to them."
Set 200 years in the future, The Expanse follows the case of a missing young woman that brings a hardened detective and a rogue ship's captain together in a race across the solar system that will expose the greatest conspiracy in human history.
Franck said he had "found a unicorn" in Adams and expected her to be an instant hit with fans of the show.
"She has a lot of range to her," he said "People in the States haven't seen her before so she'll seem new to them even though she has a lot of experience.
"I think people are going to be really excited to see her."