Dr. Kirk Langstrom poured himself into his study of bats, even though the University refused to give him more funding. His bride-to-be, Francine Lee, endured. Langstrom used himself as a test subject and it worked - his deafness was cured by using the genetics of a bat. Langstrom's transformation was not complete. Day by day, he became more and more like a bat - even physically.
Batman, while after a gang called the RidgeRunners, encountered a man in a bestial flying suit. Batman was not the bat which took the gang down. Weeks later, Alfred went to investigate an alarm in the cave. He was attacked by a huge bat creature. The Batmobile returned, placing Batman face-to-face with the Man-Bat. He was able to tranquilize the creature and strap it down to a table. There, he found the creature was once a man named Kirk Langstrom. He returned the Man-Bat to its fiancé, Francine Lee. She been working with a man on Kirk's experiments and was able to dose him with a possible antidote. After nine months outside of humanity, Langstrom was cured.