They first appeared in Marvel Boy #1 (1950) as the human-like inhabitants of the planet Uranus who became the hosts and mentors of Marvel Boy (Robert Grayson) and provided him with the technology which led to him becoming a superhero.
Uranians were originally described as a utopian society of extraterrestrials native to Uranus who had found scientific cures for aging, disease, crime, and other adversities.
The backstory of Uranos and other Uranian Eternals (such as Sui-San, mother of Thanos) was featured in Captain Marvel #29 (November 1973, by Jim Starlin).
[2] Uranos and his Eternals arrived at the seventh planet from the sun which, in fiction, became known as Uranus as a result.
Using Kree technology, the warlike Uranos and most of his followers built a spaceship with the intention to return and conquer Earth and destroy the other Eternals.