Weaver, 72, called her upcoming role as Kiri, the Na'vi adopted daughter of Avatar protagonists Jake Sully (Sam Worthington) and Neytiri (Zoe Saldaña), "goofy" in a recent discussion with Elizabeth Banks for Interview Magazine.
"So Avatar I can't really talk about, but I would say that it's the biggest stretch I get to play in every possible way," Weaver told Banks, 48, in the published discussion. "I think if Jim Cameron didn't know me really well, he wouldn't have cast me as something as goofy as this."
"I had to work in a completely different way to play this character, a very physical way," she added.
Weaver played Dr. Grace Augustine in the series' original film, 2009's Avatar. While she was long said to appear in the sequels — Augustine dies in the first movie — the details on Weaver's new role in the franchise were confirmed by Empire in January.
"I think we all pretty much remember what we were feeling as adolescents," Weaver told Empire at the time. "I certainly do. I was 5' 10" or 5' 11" when I was 11. I felt strongly that Kiri would feel awkward a lot of the time. She's searching for who she is. I was thrilled to be given that challenge by Jim."
Cameron, 68, told Empire in January that "as an acting challenge, it's big" for Weaver.
"We're gonna have a 60-something actor playing a character [decades younger than] her actual biological age," he said. "Sig thought it was all kinds of fun."
"Sigourney just became younger," Cameron added about filming Avatar: The Way of Water. "She looked younger, she had more energy, and she never quite stepped out of Kiri for our whole capture period. She had a glow on her face and lightness in her step and a fun spirit."
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In the Interview Magazine conversation with Banks, Weaver opened up about having "five projects coming out" in the near future, including the Avatar sequel.
"What's the goal going forward?" asked Banks, 48, who stars alongside Weaver in Call Jane, out Oct. 28. "I guess my point is I don't think you're retiring anytime soon."
"I would hope not, because I probably enjoy it more now than ever," Weaver replied. "I'm fine that I might be the oldest person on the set. Yes, I always have to go through a period of, 'Oh my god, it's happening again.' "
Added the three-time Oscar nominee, "But then, I get the joy and the explosion of letting this person out to live. And it's the most exhilarating thing in the world."
Avatar: The Way of Water is set to hit theaters Dec. 16, with three more untitled sequels expected in 2024, 2026 and 2028. 20th Century Studios will also re-release the original Avatar in theaters on Sept. 23.