Doctor Robert Bruce Banner, M.D., Ph.D., is a renowned scientist and a founding member of the Avengers. Highly respected for his work in Biochemistry, Nuclear Physics, and Gamma Radiation, Banner was commissioned by Thaddeus Ross to recreate the Super Soldier Serum that created Captain America. However, Ross elected not to inform Banner what he was creating. During the experiment, Banner was exposed to dangerous levels of gamma radiation (rather than vita radiation). As a result, the mild-mannered scientist found that when angered, provoked, or excited, his body and brain would transform into a huge, rage-fueled, primitive-minded creature known as Hulk.
For five years, Banner remained on the run from the United States Army, and at one point attempted suicide. When the attempt failed, he chose to live a discreet life in South America while also communicating with Samuel Sterns to cure himself. However, when General Ross sent a team led by Emil Blonsky to apprehend Banner, Banner was forced to return to New York City. He recruited the help of Betty Ross and Sterns to cure him of his affliction, but was captured shortly thereafter at Grayburn College. Blonsky, who had received a variant of the Super Soldier Serum, was administered Banner’s gamma-irradiated blood, transforming him into the Abomination. This new threat forced Ross to allow Banner to turn into Hulk and battle Blonsky, before allowing Banner to escape.