A brilliant scientist transformed by accidental exposure to gamma radiation, the super-strong, emotionally unstable man-monster known as the Hulk was a founding member of the Avengers, but was then in the midst of a gradual, long-term mental breakdown that eventually resulted in a complete split personality. 

     In his superhuman form as the Hulk, he developed a personality that was quick-tempered and primitively child-like. This led the Hulk to resign in anger following the Avengers' third mission, after the Space Phantom's impersonation of the Hulk in battle with the Avengers showed the Hulk how much his fellow Avengers feared and distrusted him.

  
     After his split with the Avengers, the Hulk's temper combined with the public's distrust of him to produce an endless series of destructive rampages that have made him a near-perpetual fugitive. He sometimes allies himself with the Avengers and other adventurers, and has formed close friendships in the Defenders, an informal super-team he helped found. For a time, the Hulk underwent a series of physical and psychological changes that enabled him to retain full human intelligence while in superhuman form, though he usually manifests one of his now several split personalities when he is in Hulk form.