Once a powerful mobster, George was arrested by Batman and sent to prison where for his crimes he recieved the death-penalty. The Mob Boss was ordered to be executed via gas-chamber filled with hydrogen-cyanide gas but before his death, a scientist transplanted George's brain with that of a gorilla. As a result, George's mind lived on within the Gorilla's body while the gorilla's mind was killed with the human body in the gas-chamber. Now calling himself "The Gorilla Boss", George decides he wants to transplant his brain into Batman's body then put Batman's brain into the gorilla's as vengeance for Batman thwarting Gorilla Boss's schemes. Now a powerful ape, Gorilla Boss fought Batman and chased him up a building only to fall off of the building onto the ground where he was knocked unconscious and Batman discovered his true identity before handing him over to the authorities.
In the New 52, Gorilla Boss was a gangster taken down by Batman and Catwoman.
In Other Media
In the Batman the Animated Series spin-off comic series The Batman Adventures, Gorilla Boss appears as a gangster super-villain. This version of Gorilla Boss is not a literal gorilla but instead wears a gorilla mask and is a member of the False Face Society where he works for Black Mask who in turn works for the enigmatic Red Hood.
Gorilla Boss appears alongside Flash Villain "Gorilla Grodd" and Doom Patrol character "Monsieur Mallah" in an episode of Batman: The Brave and the Bold where they form the organization of G.A.S.P. (Gorillas and Apes Siezing Power) in a scheme to replace Gotham's population with gorillas.