While the their shared gamma powers. The most disturbing of those ideas made genius use of Hulk's capacity to heal from anything, but in a way that's too disturbing for movie fans to ever get to see on the big screen.
Like his strength, Hulk's durability scales with his rage, often making it seem as if he's impervious to harm. However, this isn't the case, and against sufficiently dangerous opponents, Hulk is capable of taking major injuries, at which point his healing factor kicks in to repair his body. While he's not as well-known for his healing as heroes like Deadpool or Wolverine, Hulk heals incredibly quickly, and is even able to weaponize the process (for example, reassembling his body around an enemy to 'swallow' them.) Most importantly, Hulk is able to take over Bruce Banner's body and heal his injuries whenever his human side comes to harm.
Bruce turned this to grisly advantage in Absolute Carnage: Immortal Hulk (by Al Ewing and Filipe Andrade), in which the serial-killer symbiote is tracking down everyone who has ever hosted a symbiote, no matter how briefly. When the body of former Red Hulk General 'Thunderbolt' Ross is unearthed, Bruce Banner and Red Harpy (aka Betty Ross) decide to investigate but hit a logistical snag. The only way to get there in time is for Red Harpy to fly, but carrying Bruce will slow her down enough that the two fugitives are likely to be spotted. Horrifyingly, Bruce realizes he can put Hulk's healing to use to solve their problem, asking Red Harpy, "What if... You... What if you folded me up small?"
Red Harpy does as she's asked, 'folding' Bruce Banner into a convenient ball of viscera and flying him to the scene. The adventure takes place during the 'Immortal Hulk' era when Hulk emerged at night rather than in response to Bruce's emotional state. Accordingly, Bruce remains dead until the sun sets, at which point the Hulk heals their body and emerges into being. Bruce notes that "the change probably hurt much more than usual," and that due to their size difference, Hulk emerging would have been "like an airbag inflating."
While Bruce Banner rarely gets any type of credit.
While he may be known for his strength above anything else, Hulk has never needed a particularly heroic reason to lash out with violence. However, in enduring mind-bending levels of injury and torment for the greater good, Hulk is a hero in the truest sense - albeit in a way that's unlikely to get the same levels of exploration in the more family-friendly MCU.
