Bullwhip, real name Harold, was a cybernetic super villain able to extract metal whips from his wrists and was the leader of a gang of other cybernetically augmented criminals.
Bullwhip got these powers by enlisting the aid of Dr. Corso whom he met when getting a wrist replacement. He suggested to the doctor that he could get rich by using his prosthetics to make people faster and stronger. The doctor refused, saying he had all he wanted. So he and his gang kidnapped Dr. Corso's wife April and blackmailed him into making upgrades to his wrists. However, Batman got involved and the gang overpowered him the first time. After stalking them to their hideout, Batman and Dr. Corso found out that April wasn't kidnapped, but there willingly and was having an affair with Bullwhip. Dr. Corso panicked and fled. Bullwhip then briefly clashed with Batman only to have his cybernetic wrist to be severally damaged.
After Batman disabled all his teammates, Bullwhip returned to Dr. Corso, saying that if he repaired him and made even stronger, he would get April back. Corso, realizing he had total power over Bullwhip while he was under anesthesia, is heavily implied to have killed him with his drill instead.