Old Billy is a goat that lived in a pen in the countryside of Daventry until Graham enticed him to follow him with the promise of a carrot. They encountered the Bridge Troll soon after. Old Billy, hating trolls like all other goats, charged and knocked the troll into the raging river below. The carrot forgotten, the goat wandered away. It has not been seen since.
Old Billy was based on the tale of Three Billy Goats Gruff. He appeared in King's Quest I: Quest for the Crown.