Mr Banana Brain is Quackerjack's doll who is an anthropomorphized banana. He uses it as a ventriloquist dummy. He is one of Quackerjack's favorite toys. He was destroyed by Nega Duck in The Duck Knight Returns. In fact the memory is so painful to Quackerjack that he goes berserk every time someone mentions Nega Duck's name. There was another version of Mr Banana Brain made by the Quackwerks Toy Company. There's also another one in Dangerous Currency when Quackerjack is turned back from a toy.