Warning: Contains spoilers for Hulk #6 During the acclaimed Immortal Hulk series, it was revealed that, billions of years in the future, the Hulk will become a darker version of Galactus, a force of cosmic destruction, smashing planets and stars one after the other until nothing is left.
The current Hulk series also briefly showed a Hulk version of Galactus, meaning that, even if the future depicted in Immortal Hulk was supposedly avoided, this connection between the Jade Giant and the Devourer of Worlds is officially part of Marvel lore.
In Marvel's cosmology, there exists an endless cycle of destruction and rebirth, where each universe (or actually, Multiverse), is destroyed by a cataclysm and replaced by a new iteration.
This is the will of the One-Above-All, who created life but also wants to see it perpetually renewed. The last survivor of the Sixth Cosmos, Galan of Taa, was chosen by the Sentience of the Cosmos (the source of the Power Cosmic), to bond with it and become the incarnation of destruction and rebirth in the Seventh (and later the Eighth) Cosmos: the Devourer of Worlds, Galactus.Read more on screenrant.com