In the newsspaper comic, by Floyd Gottfredson, Minnie received Hoppy from an uncle in Australia. Mickey adopted him and found out he could fight! Hoppy's famous catchphrase is 'Wurp', which he says when he's ready to fight.
Mickey: That's it! Soon as he says, 'Wurp', he's ready to fight!
Mickey trains him up into a boxing champion, and he later fights with Black Pete's gorilla, and wins!