Nicole Kidman doesn't exactly have the greatest history with comic book movies. After all, her first and only was the female lead in Joel Schumacher's Batman Forever, which is widely regarded as one of the worst in the genre. Unsurprisingly, she hasn't done another one in the 21 years since, but there's a key reason why she's in the upcoming Aquaman: she's a big fan of director James Wan. As explained by producer Peter Safran,
When you look at our concept art going way back to October/September of last year, we always used [Nicole Kidman's] face for Atlanna. Before we ever had conversations with her, James [Wan] always said, 'I just picture Nicole as this.' And then, he'd say, 'By the way, I hear she wants to work with me.' And we'd all say, [sarcastically] 'Yeah, sure she does! I'm sure she loves Fast and Furious.' But when we reached out we immediately got a response, 'Oh, she loves James' work, she loves James.' So, we met with her and that was it. Just one meeting. We showed her the artwork, she read the script and she was like, 'I love this'. So, she jumped right on board.
There are few who would argue that Nicole Kidman isn't one of the best actresses of the modern era (let's not forget that she's an Oscar winner), and surely she gets script offers all the time. As such, you'd think she would react to a project such as the DCEU's Aquaman with more contemplation, taking time to consider the character and story, but apparently that really wasn't the case. Thanks to Kidman's appreciation for James Wan, it apparently took very little convincing to get her on board, and as such she is starring as Atlanna, the titular hero's Atlantis-born mother.
The above quote comes from a roundtable interview with Peter Safran on the set of Aquaman last summer in Melbourne, Australia, but I also learned that Atlanna's role in Aquaman isn't exactly gigantic. Nicole Kidman, an Australian native herself, hadn't filmed any of her scenes prior to the press day, and through our various conversations with actors and filmmakers we learned certain details about her role. Specifically, Atlanna dies before the start of the main story, punished for her relationship with the titular hero's father (played by Temuera Morrison). There will be key flashbacks, however, and it will be through those that she influences the narrative.