The Incredible HULK has come a long way since his birth in the gamma explosion. His first appearance was rather different from his current form and he was even a soulless gray color.
Eventually he grew in size and morphed into his now familiar green color. There have been several variations of the HULK from an absolute uncontrollable behemoth to the super intelligent Smart HULK
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He also managed to change to a Red version which eventually split into a totally separate HULK altogether.
He also managed to create the She HULK through a blood transfusion.
He has been part of the Avengers, Defenders and various other groups but some how the HULK has always been too big for any group.