George Harkness is an expert with boomerangs. He resorted to crime as Captain Boomerang and employs bizarre boomerang gadgets - Electro-boomerangs, Exploso-boomerangs, Gas Boomerangs, Razor Boomerangs to name a few. Boomerang's sharp tongue often puts him at odds with his fellow supervillains, mostly Deadshot. Based in Central City, he is a recurring foe of the Flash. At some point, Boomerang was recruited to serve on Task Force X in exchange for a commuted sentence.
While incarcerated, Harkness took out inmates, who intended to shiv him, in the lunchroom by using his plate like a boomerang. Soon after, Harkness woke up in familiar territory. Eager to shave more time from his sentence, Harkness immediately agreed to another Task Force X mission. He wasn't too pleased to see Deadshot again but took to flirting with Harley for old time's sake. For the mission, he posed as a paramedic delivering a corpse, Killer Frost, to the Gotham Morgue on Arkham Island. While the team crossed covertly to the intensive treatment building, Captain Boomerang failed to take out the last of four guards, who called in a unit. Deadshot had enough and grappled with Boomerang. As the team recovered and arrived at the property room, Boomerang found it absurd Harley used to work at Arkham. As she opened the property room, Harley fired back citing someone who uses boomerangs has issues with letting go. After the mission fell apart, Boomerang parted ways and raced Deadshot and Killer Frost to a police helicopter and escape the island. Deadshot shot Boomerang in the left shoulder and dumped him into several inmates. As Deadshot flew away, Boomerang swore he could get even.