The entire history of the Marvel Cinematic Universe could be changed when The Eternals, the highly anticipated cosmic drama that's currently in development, hits theaters. The possibility was broached by Marvel Studios President Kevin Feige during the Ant-Man and the Wasp press junket, when he elaborated on a potential direction for the film.
When asked by ScreenRant about the property tying into Greek mythology as writer/artist Jack Kirby envisioned when he created the series back in 1976, Feige said: "Well, one of the cool things about that property and what Jack Kirby did with it and what's been done with it in recent years is it does tie into they're called Eternals, they've been around for a long time. You know? There's this notion of all of these myths and legends that we know from ancient times, were they inspired by the Eternals?"
This could either introduce the pantheon of Greek gods to the MCU, such as Hercules and Ares, or maybe retcon the early days of mankind as it evolved. "Were they Eternals? It's a very ... you know, it's an ancient aliens kind of sci-fi trope that we think would be fun to explore someday," Feige added.
Of course, Marvel Studios has broached this subject already by painting the Asgardians as highly-evolved humanoid beings, so the Eternals could play out the same way. However, with the Inhumans present as Kree experiments in the MCU, there's also the possibility the Eternals could be kept as experiments as per the comics, instead of full-fledged aliens.
In the books, the Eternals were created a million years ago through genetic experiments by the Celestials (seen in the Guardians of the Galaxy franchise). The Eternals were imbued with the genetic potential to use their minds to control small quantities of cosmic energy. They also possess other abilities and are extremely long-lived.