No other Marvel Comics character has been so thoroughly re-imagined since their original conception as the Hulk. The character is barely recognizable from Stan Lee and Jack Kirby’s first iteration, originally published in 1962, which shouldn’t be altogether unexpected considering that what characterizes the Hulk best - in more ways than one - is transformation. Originally a surly behemoth, the Hulk has become the physical embodiment of the destructive power of rage. But perhaps one of the biggest seismic shifts in the Hulk's depiction occurred in The Immortal Hulk, when readers got to see his ultimate form.
The timeline of Al Ewing and Joe Bennett's The Immortal Hulk spans eons and features an ensemble cast of Hulk’s best known gamma mutates. In the pages of The Immortal Hulk #25, Ewing and Bennett take readers to the far, far future and introduce them to the most powerful version of Banner’s Hulk yet. The Hulk’s ultimate form is known to those who still exist in the darkening universe as “the Breaker of Worlds”. If that naming formula sounds eerily familiar to Galactus’ own epithet “the Devourer of Worlds”, there’s a reason for that.
Upon taking the throne of the Shadow Base in The Immortal Hulk #24, a tragically optimistic Hulk says, “Everything’s gonna turn out fine.” Cut to ten billion years later, and the Hulk has survived to meet the Sentience of the Cosmos, a mysterious cosmic being suggested to be responsible for the creation of Galactus. Readers are told that the Hulk will become the ninth physical incarnation of destruction, a cosmic being who ensures the continuity of the cosmos. Unfortunately for the universe, things don’t go according to plan.
Rather than merging with the Sentience of the Cosmos, the source of the Power Cosmic, Hulk devours it with green tooth and claw, the same fate which it's revealed also befell Mr. Immortal, Franklin Richards and Galactus himself. Unlike Galactus, who embodies a living force of eventual renewal belonging to a cosmic hierarchy, Hulk’s Breaker of Worlds appears set on disrupting the cosmic order and ending the known universe forever. Imagine a celestial Hulk capable of crushing suns into oblivion and tearing apart entire planets with a sweep of his hand - a being said to have consumed the Devourer of Worlds.
While the Breaker of Worlds is the Hulk's most powerful form, the story strongly suggests that Bruce Banner is no longer present in the massive body that tours the galaxy, smashing planets. More likely, the Breaker of Worlds is in some way controlled by the One Below All - a terrifying anti-god set on the obliteration of all other life, and intrinsically tied to gamma energy. Happily, the issue ends with an alien race at the end of the cosmos sending back a warning which is intercepted by Hulk enemy the Leader, so it's probably that - while Hulk assumed this form in the original timeline - Marvel's Universe may ultimately be spared a version of the Hulk whose rage is strong enough to bring about the end of all that is, making him powerful enough to literally eat Galactus.