WARNING: The following contains major spoilers for Defenders #1, available now from Marvel.
The Marvel Universe has long been home to some of the powerful forces in fiction, and few of them stand as tall as Galactus. Since he's often been presented as an elemental force of the universe's nature, the Devourer of Worlds might not seem like a complex figure, but his simple motivations belie a long and complicated history that extends back to the last incarnation of the Marvel Universe.
And in the same way that Galactus exists as a planetary predator today, Galactus' universe was destroyed by the all-consuming power of the Black Winter.
As Galactus himself explained to the God of Thunder all the way back in 1969's Thor #169 by Stan Lee and Jack Kirby, he was once an explorer known as Galan on the world of Taa during the sixth iteration of the Marvel Multiverse. He was also the final survivor of it, as his reality fell to the Creeping Plague, a force as ominous as it was menacing. Many years later, 2020's Thor #4 by Donny Cates and Nic Klein brought the Creeping Plague to the forefront of the Marvel Universe and gave it its first full appearance as the Black Winter.
With the Black Winter's arrival, certain aspects of Galactus' story came undone. While he hadn't necessarily lied about what happened to his homeworld, Galactus did leave out some particularly important information about its demise and his own rebirth. The Black Winter was far from the Eldritch sickness that he described it as. Instead, it's a being that dwarfed Galactus in every way. Where Galactus stood as the Devourer of Worlds, the Black Winter consumed entire universes, like the one that Galan had called home. To survive this cosmic slaughter, Galan made a deal with Black Winter to act as its herald in the next Multiverse. But when Galactus chose to run instead of serving out his duty, the Black Winter came to collect him. When this all came to a head, it culminated in one of the greatest battles that Thor has ever fought, one that ended in the deaths of both Galactus and the Black Winter.
While the Black Winter may be gone, the ripples of its presence are still being felt around the Marvel Universe. For one, one small piece of the Black Winter left Thor plagued by terrible visions of Thanos controlling an army of Marvel Zombies and wielding both the Infinity Stones and Mjolnir. Meanwhile, Defenders #1 by Al Ewing, Javier Rodriguez, Alvaro Lopez, and VC's Joe Caramagna has introduced another destructive force from the Sixth Cosmos through Omnimax. When Doctor Strange, the Silver Surfer and the other modern Defenders find themselves transported to Taa, they encounter Galactus' homeworld being devoured by the previously unmentioned Omnimax.
While it's not clear if Omnimax has any connection to the Black Winter, both were predatory forces that consumed on the same impossibly large scale as Galactus. In all likelihood, both had a foundational impression on Galactus that helped mold him into the universal predator that he is today.
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