There are plenty of foes that have challenged the Hulk physically, but his true psychological rival might actually be found in DC's Doom Patrol. Evidence for this can be found throughout the Immortal Hulk series from Al Ewing and Joe Bennett.
A big reoccurring question in the saga of the Hulk is who he really is. Some wonder if the Hulk is the true persona and Bruce Banner merely some identity the Hulk hides inside of. The Immortal Hulk takes this idea and pushes it to its limit. Throughout the series, the Hulk and Bruce Banner take on many different forms, not just physically but psychologically as well. Bruce Banner essentially suffers from what could be called dissociative identity disorder. There are many versions of the Hulk within him and each can have control at different times regardless of the physical form the being known as Bruce Banner has taken.
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Because of this, the perfect adversary for the Hulk is not some big, muscle-bound mutant. Instead, the Hulk would be perfectly challenged by Crazy Jane of the Doom Patrol. Jane, who is inhabited by dozens of split personalities, constantly struggles with different personas taking over her body. Even Jane herself is a fabricated persona. What makes her even more dangerous is the fact that each persona has its own superpower. So if Hulk and Crazy Jane were ever to face off, it's possible that each of them could be shifting back and forth between their different identities while battling one another in a fight that is just as psychological as it would be physical.
The similarities between the two characters also go a little deeper. Although her origins are slightly different in the Doom Patrol
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