Dr. Kirk Langstrum created a serum that hopefully would give a human a bat's sonar abilities, he hoped it would cure him being deaf. It worked too well as he transformed into a half human half bat monster known as Man-Bat! Batman would have to fight him several times & capture to cure him.
I am the reason you are friends
I am the reason life is fun
I am adorable...and...
I am the kindness.