Dr. Robert Bruce Banner, Ph.D.[4] a.k.a. the Hulk, is an American theoretical physicist, famed for his work in the fields of nuclear physics and gamma radiation.[63] He was recruited by General Thaddeus E. "Thunderbolt" Ross and the U.S. Army to develop the first Gamma Bomb. During its first live test he was bombarded with a massive dose of gamma rays while saving Rick Jones, a kid who had made his way onto the test site. He was mutated into a green behemoth, the living personification of rage, fueled by pure physical strength and would come to be known as the near-mindless "Incredible Hulk". Fearful of the damage that Hulk could inflict, as well as fleeing from the military, he went on the run.[64] In the years that followed, Bruce became a loner, occasionally joining together with other heroes but more often struggling to be left alone. He was a founding member of the Avengers, "Earth's Mightiest Heroes", as well as the group of outsider heroes known as the Defenders, but would not remain with either group for long.[37][65] Over the years, the Hulk's personality changed drastically, owing to Banner's undiagnosed dissociative identity disorder. At times intelligent, other times savage, the one constant was his quest for solitude and peace in a world that would not leave him alone.[64]