WARNING: The following contains spoilers for Eternals, in theaters now.
Around halfway through Eternals, it is revealed that the film's superpowered protagonists are not living beings from the planet Olympia as they were programmed to believe but are, in fact, advanced robots designed by the Celestials in the World Forge for the sake of fighting off the malfunctioning Deviant robots and helping planets give birth to new Celestials. Sersi, the Eternal chosen the lead the group after Ajak is murdered, is the one who first learns this truth from the Celestial Arishem. And in retrospect, the casting of Gemma Chan as Sersi could be seen as a subtle foreshadowing of this twist.
Chan's breakout acting role happens to have been another intelligent android, Mia, from the Channel 4/AMC sci-fi series Humans. Like Sersi and the other Eternals, Mia is first introduced with her memories wiped, programmed into the subservient maid robot Anita. By the end of Humans' first season, Mia's true identity as the first fully conscious synth is recovered from within her code, and by the end of the series, Mia is able to use her full knowledge to become a sacrificial hero who makes peace between humans and synths.
It's been said that director Chloé Zhao approached the all-star cast of Eternals similarly to the way she did the unprofessional actors in her earlier indie dramas, casting people because she wanted them to play themselves. With professional actors, however, knowledge of past performances will inevitably inform casting as much as knowledge of their personal lives.
Casting Chan, who gave an incredible performance as an artificial intelligence recovering her memories in Humans, to play an artificial intelligence recovering her memories in Eternals feels like an intentional bit of typecasting as a result. Her talent at playing this particular character archetype helps explain why she ended up being cast as Sersi, despite already having another role in the Marvel Cinematic Universe as Minn-Erva in Captain Marvel.
If the casting of Sersi is an intentional piece of foreshadowing, it's not one that viewers will be thinking about before the ultimate reveal of the "Eternals are robots" twist. After the reveal, however, it becomes more obvious and will have fans of Humans thinking about the parallels between Mia and Sersi.
See Sersi and the other Eternals in action in Marvel Studios' Eternals, now in theaters.