Earth-2013

Earth-2013 is a universe where the characters of Steven Universe co-exist with those of Marvel Comics, most notably the Avengers, Guardians of the Galaxy, X-Men, Fantastic Four and many others.

History
Earth-2013 is like any other part of the Marvel multiverse and shares similarities with other universes like Earth-616 (the main comics universe), Earth-199999 (the setting of the Marvel Cinematic Universe) & Earth-8093 (The Avengers: Earth's Mightiest Heroes series) but the biggest differences is the presence of the alien lifeforms known as Gems. They resemble human females in form but their defining features are more colorful skin and gemstones on their bodies. Although they had a major presence in Earth's history, many humans were unaware of their existence.

Hailing from the enigmatic Gem Homeworld, the Gems had a large hold on many parts of the universe for producing weapons and more of their kind, under the rule of the Great Diamond Authority. When one of them named Pink Diamond was assigned Earth as her first colony, she grew to appreciate the creatures inhabiting it and decided to protect it by faking her own demise and masquerading as a Rose Quartz.

Forming the Crystal Gems alongside her Pearl, a fusion of a Ruby & Sapphire known as Garnet and a Bismuth, Rose made alliances with the Ancient Panther Tribe of Wakanda, the gods of Asgard, the Inhumans, the warriors of both Atlantis & K'un-Lun, the followers of En Sabah nur and the Masters of the Mystic Arts to combat Homeworld in a war that lasted for thousands of years.

Also involved in the war was the Mad Titan Thanos, who wanted to obtain the Infinity Stones to gain ultimate power over life & death and win the favor of Lady Death by purging half the universe to save it. He sided with neither of them in the Rebellion as he had a hatred for all Gemkind due to Pink Diamond's own Jasper rejecting his offer of forming his own alliance with Homeworld to find the Stones.

Although Rose's alliance had won the war, it came at the cost of many of their soldiers dying in the conflict and most of the Gems present becoming corrupted in one final attack by the Diamonds. Thousands of years later Rose, Garnet and Pearl, the remnants of the Crystal Gems, now joined by an overcooked quartz Gem named Amethyst, began hiding out in a town that would become Beach City.

Occasionally they would venture out into the world crossing paths with Dr. Abraham Eskrine, Holocaust survivor Erik Lehnsherr, young would-be soldier Steve Rogers & his best friend Bucky Barnes, war veteran Nick Fury, mutant rights activist Charles Xavier and genius billionare Howard Stark. Eventually Rose met and fell in love with a young rockstar named Greg, even producing a son that Rose had to give up her physical form for him to exist. The baby was then named Steven.

Meanwhile the Avengers were formed in 2008 and originally consisted of the sentinel of freedom Captain America, the invincible armored Iron Man, Thor Odinson the prince of Asgard, the Incredible Hulk, super-spy Black Widow and master sharpshooter Hawkeye. Over the years more superheroes were added to their ranks like genius scientist Hank Pym aka Ant-Man & his partner the Wasp, King T'Challa the Black Panther, the Sorcerer Supreme Doctor Strange, Carol Danvers aka Captain Marvel, the mutants Wolverine, Scarlet Witch & Quicksilver, the android Vision and the amazing Spider-Man.

The Avengers fought many foes over time like the mad god Loki, the villainous machine Ultron, Baron Zemo & the Masters of Evil and Thanos. Growing up, Steven idolized these heroes and wanted to be like them when he was older, especially Captain America. Then one day he actually met a group of real heroes. They were Star-Lord, Gamora, Drax the Destroyer, Rocket Raccon and Groot, the Guardians of the Galaxy. That was how some of his most marvelous adventures began.