Secretly the illegitimate son of an American soldier and an Australian woman, Harkness was raised in an Australian town called Korumburra in poverty, during which time he developed great skill in making boomerangs, and in using them as weapons. As a young adult, he was hired as a performer and boomerang promoter by a toy company which was, unbeknownst to him, owned by his biological father. It was at this time that he developed the Captain Boomerang persona that he would continue to use in his later criminal career. Audiences ridiculed him, and a resentful Harkness turned to using his boomerangs for crime.