Marvel's famous of deleted scenes in the franchise) would have fixed many problems that audiences found with the film - but the source material of the scene was far darker than anything the MCU would show on screen for many years.
Director Louis Leterrier initially opened his film with a sequence (now deleted) in which Bruce Banner hikes across the Arctic by himself. He carries minimal supplies and is accompanied only by a dramatic string section, courtesy of composer Craig Armstrong. When he decides he's far enough away from civilization, Bruce produces a revolver - but before he can pull the trigger, his eyes shine bright green and the Hulk emerges, roaring and causing an avalanche.
While the scene ended up on the cutting room floor and was thus rendered non-canon, Bruce's suicide attempted was later mentioned in The Avengers. "I got low. I didn't see an end, so I put a bullet in my mouth and the other guy spit it out." The moment is appropriately dark in the film (even more so when one realizes Banner was about to be escorted to a cell which was designed specifically to kill him), but it's based on the 2001 book Startling Stories: Banner #1, and in this instance, the Hulk didn't merely trek across the Arctic - he destroyed an entire city.
At the end of the issue when Banner realizes exactly what he's done and the level of destruction he has accomplished (military pilots hovering over the devastation in a helicopter even refer to the Hulk as a "bomb"), Bruce wanders onto a mountain alone and asks for forgiveness...for everything he's done, and what he's about to do. He puts a revolver inside his mouth and pulls the trigger - but readers don't see the aftermath of Banner's suicide attempt until the next issue, when the Hulk angrily spits out the bullet. In the film, readers never saw exactly what drove Banner to attempt suicide, but the book details every inch of the Hulk's destruction.
The art in Startling Stories: Banner #1 gives one an uneasy feeling when they look upon the Hulk; the creature appears angry and at the same time completely helpless. As the "Savage Hulk" Banner has the mind of a young child and his only want is to be left alone. The Incredible Hulk, while a very dark MCU film by the standards of the series, never quite rose to the level of darkness that the Hulk saw in the comics.
