Almost half of the Ultimates' original line-up consisted of people who gained powers while attempting to recreate the serum that gave Captain America his original powers during World War II. Hank Pym's experiments resulted in him being able to grow to giant sizes, and his wife shrink to the size of a wasp (hence her nickname, the Wasp). Later, it was discovered that Wasp was actually a mutant and Hank just used her powers to reverse-engineer his growth abilities. Dr. Bruce Banner was slightly more talented, and his attempts to replicate the original Super Soldier Serum led to him creating a formula that he tested on himself. Instead of making him a Super Soldier, it instead turned him into the rampaging green monster known as the Hulk.
When the actual Captain America is found and the Ultimates were formed, Banner's curiosity got the better of him, and in “Ultimates” #4, he injected himself with a mixture of his formula and Captain America's blood (which they now had ample supplies of). The resulting formula transformed him into the even more monstrous and powerful gray skinned Hulk.He then went on a monstrous rampage in New York City, angry that Banner's ex, Betty, was dating Freddy Prinze, Jr. The Ultimates found themselves on their very first mission – to take down one of their own!
Writer Mark Millar and especially artist Bryan Hitch went to town with the battle in “Ultimates” #5. Each of the Ultimates took a turn with the Hulk and he handled each of them pretty easily. First he teaches Giant-Man about the whole "the bigger they are, the harder they fall" routine. The Wasp distracts him for a second with one of the more unusual fighting techniques – she flashes her breasts at him. This sets up Iron Man's battle with the Hulk, which does not end well for Iron Man.
The whole time, the battle is doing tremendous property damage to New York.
Surprisingly, Captain America manages to hold his own against the rampaging behemoth, especially as Cap is not particularly inclined to fight fair, including a kick to the groin.
Ultimately, it is the Wasp who saves the day by crawling into the Hulk's ear and using her sting power to blast his skull repeatedly from the inside until he collapses and reverts back to Bruce Banner. As SHIELD agents come by to arrest him, Captain America gets in one last shot, kicking the helpless Banner in the face.
The Ultimates had faced their first public battle and came out on top!