Thanos among them. So how exactly does the Mad Titan connect with the Eternals? The answer actually lies in the Eternals’ longtime foes — the Deviants!
The Eternals and the Deviants first appeared in 1976’s The Eternals #1 and were created by the legendary Jack Kirby, who was returning to Marvel after a brief but memorable stint at DC. Both the Deviants and the Eternals share a common origin. Many millions of years ago, inspire the stories of gods, goddesses and monsters on Earth.
Thanos' parents A’lars and Sui-San were both Eternals, who lived on Titan, a moon of Saturn. Since his parents were Eternals, this means Thanos should not look as grotesque as he does, but thanks to some recessive genes carrying Deviant DNA, he was born deformed, much like a Deviant would be; furthermore, Thanos’ murderous and deceitful nature is more in line with the way many Deviants act as well. However, Thanos also reaps the benefits of his parents being Eternals — namely his fantastic array of powers, including the constitution necessary to use the Infinity Stones.
The Deviants’ reign of evil stretches beyond Thanos however. The Skrulls, the shape-shifting extraterrestrials that have invaded Earth on several occasions, are also considered Deviants; the Celestials performed their genetic manipulations on the species that would become the Skrulls, and the Deviant strain borne of those experiments became the dominant of the two. So, in a way, the universe-destroying psychopath Thanos is related to the genocidal Skrulls (a fact which also explains why he shares their distinctive ridged chin.)
Of course, while Deviant DNA can often produce psychotic, incredibly powerful monstrosities, it's not inherently evil, though the fact that it turns individual Deviants into such unique creatures they're considered a species of one does often put them at odds with the other species with which they share a planet. Sadly, no accident of genetics turned Thanos into the monster so many Marvel fans love to hate, though the Eternals reaction to his Deviant physiology did help push him away from society and into the madness that still powers this terrifying villain.
