Anton Knight was the son of Gotham City gangster Charles Knight. Spoiled by his father's ill-gotten wealth, Anton grew tired of Gotham and left the city to travel to the Orient, where he trained in the martial arts.He continued to correspond with his father and soon learned of the young girl Natalia, whom the elder Knight had taken off the streets and "adopted." The combination of his father's letters and his own romantic nature led Anton to fall in love with his foster sister, even though they had yet to meet.
A few years later, when Anton heard of his father's death, he returned to Gotham and vowed to love Natalia. They dedicated themselves to the "elegance of the night" and Anton donned a black costume and became the Night Thief, so that Natalia would always be surrounded by elegance.As the Night Thief, Anton often came into conflict with Batman, but always managed to escape from the Caped Crusader by disappearing into the Gotham shadows that were commonly thought to be Batman's domain. Finally, however, Anton was captured by Batman in a room full of bright lights.
Anton was sent to prison, after Natalia failed to free him, but he managed to escape on his own during a storm. He returned to Natalia and overheard her new partner, Sturges Hellstrom, trying to seduce her. Furious, Anton killed Hellstrom but found to his own horror that Natalia would have nothing more to do with him. She accused him of "slaying the night magic" and their love. Anton in turn felt slain by her words and he left her. However, he soon returned to find his former lover in the arms of Batman. He attempted to kill Batman and might have succeeded if Natalia hadn't shot him. Anton barely escaped with his life.
After recuperating, Anton - now known as Nightslayer- attempted to kill Batman and Natalia again, failed again and escaped into the night. Next time he appeared, he was completely deranged. He went on a killing spree in his renewed attempts to find and murder Natalia Knight. Despite the best efforts of Batman, Robin and Catwoman, he succeeded in stabbing Natalia before he was apprehended.
Anton was the son of one of Nocturna's many husbands and is thus her step-son. Anton and Nocturna struck up a romantic relationship themselves, and he adopted the identity of "Night-Thief" in order to aid Nocturna in her crimes.
Recently, the assassin Killshot was hired to murder Nocturna, and Night-Thief jumped in the way of several bullets intended for his love. Anton stumbled over the edge of a building and began to fall into the river bank. Nocturna caught Anton but she fell into the river with him. Its possible that Anton died from his gunshot wounds since Nocturna has chosen Batwoman as her new lover.