Bruce Banner worked as a scientist on the gamma bomb project when he heroically saved a young man from exposure to a nuclear blast. Unfortunately, the exposure to gamma radiation changed Banner's cell structure, causing him to transform into a raging green monster (known as the Hulk) when he became angry.Marvel Source
Over the years, the Hulk has acted as hero, villain, or pure destructive force depending on his state of mind.
Through it all, Banner continues to search for a cure that would end his deadly rampages.
10/3/13 Update - 5 points move from Hulk Tough to Earthquake leap; felt Hulk was already survivable enough without those 5 points in armor boosting passive and would do better in more damage. Mighty Smash removed. Been spending too much time in MM/Cow, preferring PBAoE more now. Points added to Terrible Roar for even more damage.