When speaking technically about Marvel parallel universes, it’s important to note that the Marvel Cinematic Universe was an alternate reality branching off from Marvel Comics the moment it came into existence - but now the Marvel Cinematic Multiverse has officially been born, and things are about to get weird. For regular readers of Marvel Comics, however, alternate realities/timelines/dimensions are old hat. In fact, some of their favorite characters come from them.
The original, mainstream, and definitive Marvel Universe is known as Earth-616, and that’s where most, but not all, Marvel Comics stories take place. But in a multiverse where interdimensional travel is commonplace, adventurers from other Marvel Earths regularly make their way to Earth-616. Some are just paying a visit. Others end up sticking around a lot longer than that.
Home Universe: Earth-1610
The Ultimate Universe was, in real-world terms, a parallel publishing line in which Marvel Comics attempted to modernize its classic characters in a brand-new continuity. In comic book terms, it was just another alternate reality. The basic idea was that, in the Ultimate Universe, characters could change, grow old, and even perish. Inevitably, then, that very fate befell its biggest star, the Ultimate Spider-Man.
Shortly after the demise of Ultimate Peter Parker, a new Spidey started slinging webs in Earth-1610 after being empowered by the same sort of experimental spider that once bit Parker. His name was Miles Morales, and he quickly became so popular that the thought of him not making it over to Earth-616 eventually was inconceivable.
Through a couple of interdimensional fracases, Miles got to meet the original Peter Parker and visit Earth-616, but even that wasn’t enough. Finally, the Secret Wars mega-event saw Morales improbably survive the end of the Marvel Multiverse - though the Ultimate Universe itself did not. During the course of exploring Battleworld, he gave a cheeseburger to a hungry Molecule Man and then, later, while the Molecule Man was helping Reed Richards rebuild the Multiverse, he returned the favor by slotting Miles, his family, and his closest friends into the refurbished Earth-616. For a time, Miles was blissfully unaware of his true origins, though he later learned of them from Madame Web.
Now, there are simply two Spider-Men in the mainstream Marvel Universe, and everyone is just fine with that.
The Maker Is An Evil Alternate Reed Richards Turned Loose On Earth-616
Home Universe: Earth-1610
The Ultimate Universe was created as a parallel publishing line in which Marvel Comics could condense, update, and really muck with the stories of their most cherished characters. Some heroes remained more or less the same in Earth-1610, but others went off on wildly different paths - perhaps none more so than Ultimate Reed Richards, who became the genocidal villain known as the Maker.
Breaking bad when Sue Storm rejected him, the Maker used his elasticity abilities to grow his brain to a disturbing size, then set about conquering the world. He nearly succeeded on at least two separate occasions before being defeated and hired on by S.H.I.E.L.D. as a tenuous consultant.
That put the Maker in a position to first understand, and then survive, the end of the Marvel Multiverse. And though he later tried to usurp the power that the Reed Richards of Earth-616 would use to rebuild the Multiverse, the Maker was still gifted with a home on Earth-616 when it was all said and done. There, he’d go on to battle Sunspot, the Ultimates, and the Future Foundation before joining the Interdimensional Council of Reed Richardses and setting his sights on the restoration of Earth-1610.
Home Universe: Earth-616 of the Sixth Cosmos
Galan of Taa was a scientist living in the Earth-616 reality of the Sixth Cosmos, better known as the multiverse directly preceding the first modern Marvel Multiverse. Facing annihilation at the hands of either the Black Winter or the Big Crunch - sources differ - Galan proposed a last-ditch effort to go out in a blaze of glory, and somehow ended up the only surviving member of his reality.
Combining with the ashes of the Sixth Cosmos, Galan also managed to survive the creation of the Seventh Cosmos and arose there in a new form: that of Galactus, the Devourer of Worlds. Now one of the Marvel Multiverse’s most foundational entities, Galactus began performing the unsightly, but necessary, task of eating planets, and he’s more or less been doing so ever since - give or take a few brief absences. Countless planets have trembled under the gaze of the World Devourer and fallen.
Galactus hasn’t yet managed to consume the planet that gives Earth-616 its name, but not for lack of trying.
Home Universe: Earth-65
The Gwen Stacy of Earth-65 first appeared, like many alternate Spider-People, in the opening pages of the first Spider-Verse event. In her world, it was she who was bitten by a radioactive spider instead of Peter Parker - who, in turn, perished tragically in her stead.
Officially known as Spider-Woman, but more frequently called Spider-Gwen, Stacy joined together with her webslinging compatriots to oppose the Inheritors and protect the Web of Life and Destiny on numerous occasions, becoming a founding member of the Web-Warriors. When the Web was brought down by a rogue Spider-Man, Gwen became the only Web-Warrior still capable of traveling to different dimensions through the use of a modified Dimensional Travel Watch.
Due to her strong bonds with Miles Morales and Jessica Drew, both of whom call Earth-616 home, Gwen began to spend more time there than in her home dimension, and eventually made the full-time move. Now, she attends Empire State University alongside Miles and regularly teams up with the Order of the Web, so it looks like she’s there to stay.