The Mad Titan, Thanos, could sneak his way back into the Marvel Cinematic Universe through Eternals, which could be a terrific way to bring in more of Thanos' comic history. Fans saw a memory of Titan during Infinity War, but Thanos' backstory is very limited in the MCU at this moment. However, Eternals could explore more of his history given Thanos' complicated origins in relation to Titan and the Eternals.
Thanos in the films and comics is from the once-idyllic world Titan, which was first introduced in 1973's The Invincible Iron Man #55, written and drawn by Jim Starlin; this was also the first introduction of the Mad Titan. Meanwhile, Jack Kirby introduced the Eternals and their Celestial masters to Marvel in 1976, but he would never draw Thanos. These two separate worlds finally came together under writer Roger Stern and artist Al Milgrom, who made Titan into another world of the Eternals in Avengers #246.
Once that tie was established, Thanos' backstory bloomed, with the comics diving into his childhood, as well as the pathos that comes with the life of an outcast. Thanos is the child of Titanian Eternals, and he almost didn't survive his birth. His mother, the Eternal Sui-San, recognized that the purple-skinned child carried the Deviant gene, making him a mutant Eternal. For Eternals, the Deviants are enemies, but Sui-San's mate, A'lars, stopped his lover from killing their son, and Thanos had a surprisingly peaceful childhood until he discovered his nihilistic obsession with death.
In both the MCU and comics, Thanos is the doom of Titan. While his film motivation is driven by his delusional notions about balance, 2013's Thanos Rising, written by Jason Aaron with art by Simone Bianchi, grants him a simpler purpose, and Thanos' actions don't assuage the Eternals' distrust of Deviants.
The Celestials went from world to world, engineering Deviants and Eternals, and if the Celestials are displeased with the results of their experiment, that world is purged. For the Eternals, they believe it means that the Deviants are imbalance incarnate. Seeing themselves as caretakers, Eternals "weed out" the Deviants, so Sui-San's frenzy at the sight of her Deviant baby makes tragic sense.
As the key villain of the MCU's first three phases, it's not likely the franchise will return Thanos to prominence any time soon. Though the multiverse makes it possible for him to come back, it's likelier that Eternals could visit him through flashbacks, exploring the dynamics between the two races. Thanos is already known to MCU audiences, and he could become vital in explaining the animosity between Deviants and Eternals.
Thanos' obsession with balance went without deeper explanation in the first phases of the MCU, but Eternals could give him a clearer purpose. As an outcast ignored despite his Eternal heritage, his warped notion of balance could tie to his dueling Eternal and Deviant identities. It would be a useful commentary on today's Eternals, as well as the danger they're certain that unchecked Deviants could pose.
Directed by Chloé Zhao, Eternals stars Gemma Chan as Sersi, Richard Madden as Ikaris, Kumail Nanjiani as Kingo, Lauren Ridloff as Makkari, Brian Tyree Henry as Phastos, Salma Hayek as Ajak, Lia McHugh as Sprite, Don Lee as Gilgamesh, Angelina Jolie as Thena, Barry Keoghan as Druig and Kit Harington as Dane Whitman/Black Knight. The film arrives in theaters Nov. 5.