Mindless Hulk occurred when the dream demon Nightmare tried to impact upon Doctor Strange by attacking his ally in Banner. Through psychic penetration, Nightmare manipulated the worst thoughts and feelings Banner had about Hulk to create the most terrible version of the monster. Separately, Devil Hulk is the manifestation of Banner’s resentment, while Guilt Hulk – also known as The Beast – is the embodiment of Banner’s regrets.
Maestro is a future Hulk that has been strengthened by the same nuclear devastation that has supposedly wiped out all other heroes and villains, while Doc Green is the result of a Hulk being exposed to Extremis (a procedure seen in Iron Man 3, as well as the comic books). Finally, Green Scar is the embodiment of the need to survive, which manifests when Hulk is on the planet Sakaar, and World Breaker Hulk is a more focused, powerful version of the same.
This is the true beauty of The Incredible Hulk. He’s unique in comic books in that he provides a real exploration of the human emotional experience through the depiction of a character living with a mental health condition. Hulk is the physical externalization of Banner’s stresses and emotional responses – and the damage he wreaks upon his environment is analogous to the psychological damage from which he’s seeking to protect himself. That Banner has been highly successful in his chosen professional field while dealing with this cognitive turmoil is worthy of note – as is the fact that he takes this emotional dysfunction and uses it for largely heroic purposes.
But, there is a further level of function for this iconic character, too. Hulk is one of the clearest examples of a pop culture response to the threat of nuclear destruction. He was created just as the reality of the atomic age was beginning to settle in with the average world citizen, and as global political tensions with foreign nuclear powers were reaching fever pitch. While many comic book superheroes were created through terrible accidents with dangerous chemicals and energies, it’s Dr. Bruce Banner who literally saved a younger generation by throwing himself in front of a radiation blast.
Little of these fundamental aspects of his character have been seen outside of the Marvel comic books, though. Instead, to date, we’ve been handed the same basic Hulk variation time and again.