Told by a doctor he had only six months to live, William Tockman became distraught, worrying about who would take care of his invalid sister after his death. Refusing to have his sister turned over to a state nursing home, yet having no insurance or savings of his own, Tockman decided to turn to crime to provide money for his sister's future, reasoning that even if he was caught, he'd never live long enough to serve any time. Since time was running out for him, Tockman was determined to make use of every second. Taking the clock, the symbol of time, as his own symbol, Tockman used his expert knowledge of clocks to become the Clock King.

The Clock King's series of time-related crimes quickly brought him to the attention of Star City's crimebusters Green Arrow and Speedy, and after a series of dangerous encounters, the ace archers finally defeated the Clock King and turned him over to the authorities.

While in prison awaiting trial, Tockman suffered the ultimate irony when he learned that he wasn't dying after all; his doctor had accidentally switched Tockman's lab reports with those of another patient. Since Tockman was no longer free to take care of his invalid sister, she was placed in a state nursing home, where she eventually succumbed to her illness. Tormented by his sister's death, Tockman swore to avenge himself on his incompetent doctor and the Green Arrow, and he has escaped from prison several times over the years in a vain attempt to carry out his threat.