Think of him as a 2 year old, with the strength to literally lift a mountain. When angry, he is the scariest thing in the world. In the Marvel Ultimate Universe he has even engaged in rape and cannibalism, regularly ripping people’s heads off, as well as plain wanton. However when he is not enraged, he can be kind and gentle; there are many comic book scenes with hulk and forest creatures (think Disney Snow White and the birdies).

This is the appeal of the Hulk as a character, the contrast between extremes.

..and yes, it is Banner’s fear of the Hulk that essentially makes him uncontrollable. The best analysis I have ever heard is that Banner is actually a trauma induced schizophrenic. He does not so much as get mad then transform into the Hulk and gain power, but slip into a different personality willing to use the power of the Hulk that always exists in Banner.