During the 2004 storyline Identity Crisis, George Harkness is killed and his son, Owen Mercer (also known as Owen Harkness), takes over his father's role as Captain Boomerang for a period of time until his own death. Following the 2009–2010 Blackest Night storyline, George Harkness returns to life and returns as Captain Boomerang. Following 2016's DC Rebirth, the George Harkness incarnation of Captain Boomerang is part of the supervillain team Suicide Squad in the fifth volume of the team's eponymous comic book series.
Digger Harkness first appeared in The Flash #117 (December 1960) and was created by writer John Broome and artist Carmine Infantino. Throughout the first several years of the character's existence, Captain Boomerang spoke with an American accent. Beginning in the late 1980s, he developed an Australian accent.
Secretly the illegitimate son of an American soldier and an Australian woman, Harkness was raised in an Australian town called Leongatha 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.
When he began committing crimes, he threw suspicion off of himself by briefly pretending another man was impersonating him, showing his 'parents', (really other crooks) to the Flash after the Flash caught him next to a crime scene. He nearly succeeded in killing the Flash after knocking him out with a boomerang, then tying him to a giant boomerang that he fired, which then got sent into space and then fell into the ocean. However, the Flash was able to escape from his friction-proof bonds by quickly vibrating his molecules. He also increased the boomerang's velocity so much he was able to use it to defeat and jail Harkness and the two crooks.
He became a recurring enemy of the Flash, typically by devising altered boomerangs which could produce astonishing effects (some would explode, others had razor-sharp edges, etc.), and using them ruthlessly. He became a staple member of the Rogues, a group of villains dedicated to opposing Flash, and who were first organized after Gorilla Grodd broke them out of jail. Though captured when Flash made their weapons hit each other, they continued to act together.