Hulk and Banner are not the same person.
MPD = Multiple Personality Disorder. That's what Banner has. One cannot control the other.
Do you want to understand the Hulk? Check out Giant Size Hulk #1 (it came out in June or July or something). Also check out Hulk #100 (this came out a few months ago). You really just have to read some Hulk to truly understand him.
Anyway, here's a story to Help that comes from Giant Size Hulk #1:
The Champions (a team consisting of Ghost Rider, Hercules, Black Widow, and some others) see Hulk jumping across the city carrying a car. They attack him, trying to stop him. They all beat up on him but they don't bring him down because he just swats them away and keeps going. The entire time he doesn't drop the car. He finally stops at a hospital and takes a girl out of the car and gets a doctor. She had appendicitus and would have died if he was five minutes later. Hulk jumps away and the Champions let him go.
Hercules and the others talk to the womann and she explains that they were stuck in traffic so Bruce Banner turned into the Hulk to get her to the ER in time. Hercules says, "Well, if that's what he was trying to do why didn't he just say so?" She looks at him, looking super pissed, and says, "Did you ASK?"
And that's how it is a lot of the time. If you read those two comics you will understand a LOT more about the character.
Hulk isn't a villain. End of story.