It’s hard to make a corporately-owned superhero intellectual property something distinct. The temptation is to generally keep the character in the form fans recognize him or her in the most and try to give him or her some exciting adventures to please the fans. In fact, the more high profile the character, the less editorial is going to allow a certain level of meddling. Second and third stringers can be used for that sort of thing.
That’s sort of what makes the Hulk a unique character. Though often depicted as just a big, stupid brute who doesn’t understand how to use personal pronouns, the Hulk has often been used as a more experimental character, someone whose intelligence and setting can fluctuate depending on the story’s needs. The Hulk is high profile enough for Marvel to always have a Hulk book of some kind in publication, but not enough for them to really care as much about what he’s doing as they are, say, Spider-Man. That’s led to some interesting Hulk runs and experiments in the character. Writer Peter David played with the idea Bruce Banner had Multiple Personality Disorder and had different Hulks appearing at different times until Doc Samson figured out how to merge them into a composite being that was always the Hulk. Paul Jenkins developed this concept further, and had a run complicated by Bruce contracting Lou Gehrig’s disease and needing to find some sort of cure before he had to become the Hulk permanently. Even Bruce Jones, a writer whose comics I don’t much care for, initially had an interesting run where Banner was on the run from some conspiracy that seemed supervast and complex until Jones wrapped the whole thing up in two issues by saying it was just the Leader the whole time, which ended something cool in a lame manner.
And then there’s the Planet Hulk storyline, which may have been one of the most ambitious Hulk storylines ever done.