The Hulk has had many different forms over his history in Marvel Comics, from the classic Savage Hulk to the Spartacus-like Green Scar, but his most disgusting form came courtesy of the mysterious seventh Infinity Stone, the Ego Stone. While Bruce Banner has always loathed his transformation into the Hulk, this 'Ghoul' form added a haunting new aspect to the Green Goliath's status quo.
While the first six Infinity Stones embody different aspects of the foundational forces of the universe, the seventh is slightly different. In Marvel lore, the Stones began as a single, godlike being who was shattered into separate parts. The Ego Stone retained the consciousness of this being, and sought to gather the other Stones back into a single form as the being known as Nemesis. To do this, the Ego Stone had to extend its reach across both the Marvel Universe and the Ultraverse (a different comic book world published by Malibu Comics), bringing the Avengers and heroic team Ultraforce together in a brutally literal way.
When the Avengers and Ultraforce team up to confront Nemesis, the mad god uses the power of the gathered Infinity Stones to destroy them. However, because the Stones are inherently bound to the act of creation, they don't simply eradicate the assembled heroes. Instead, they create a new multiverse full of worlds that combine Marvel and Ultraverse history in different ways. While some heroes like Iron Man arguably get upgrades from this process, the most tragic victim is the Hulk. In Ultraforce/Avengers #1 - from Warren Ellis and George Perez - fans meet the new version of the hero, whose history has been combined with the Ultraverse zombie known as Ghoul. Ghoul is an undead being, and combining his body with that of the Hulk creates a monstrosity that the comic notes is in constant pain, driving him to new heights of rage. With a half-formed exoskeleton and sloughing skin, this Hulk is described as a "half-dead, irradiated, tumorescent THING that was once a nuclear scientist.
Hulk is a tragic figure at the best of times, regarded as a monster by the wider world and subjected to cruelty and violence in a cycle of pain and recrimination. However, fusing with Ghoul finally internalizes this process, as Hulk's rage is no longer motivated by external factors, but by constant physical pain he can't control. Unlike the other heroes, Hulk doesn't get many benefits to this merging, as Ghoul's 'healing factor,' poison & radiation immunity, and ability to commune with the dead are powers Bruce Banner already has. Given the rage born of his suffering, the Ghoul Hulk is at least likely among the strongest Hulks in any reality.
In Marvel lore, the Hulk persona developed during Bruce Banner's childhood to face the pain dealt out by his abusive father, later taking physical form once he was inundated with gamma energy. Al Ewing and Joe Bennett's Immortal Hulk confirmed that the classic Hulk is effectively still a child - one who lashes out because he sincerely doesn't understand why he seems to exist solely to soak up the pain of another being. With this in mind, the Ghoul Hulk is even more horrifying, robbing the childlike Hulk of the brief moments of peace and connection he's been able to find in the regular Marvel Universe. Thankfully for the world, this version of Hulk at least manages to fulfill his original role of being the threat the Avengers first assemble to confront (thought this fight goes far more tragically, costing Hank Pym's life), which means there is a team present to take the fight to Nemesis and destroy the Ego Stone, resetting reality to its original form.
The core tragedy of the Hulk is that a being who has the potential to be at peace is constantly embroiled in conflict, acting on heroic instincts in a world which will nevertheless never stop hounding him. With a cruelty born of cosmic insight, the seventh Infinity Stone made that tragedy definitive by taking the pain Hulk is doomed to suffer and - by trapping him in a rotting, tortured zombie body - making it an inescapable part of his nature.