Dr. Kirk Langstrom, a scientist specializing in the study of bats, develops an extract that is intended to give humans a bat's sonar sense and then tests the formula on himself because he is becoming deaf. While the extract works, it has a horrible side effect: transforming him gradually into a hideous human bat in Detective Comics #400 (December 1970) - Man-Bat also received his own short-lived series several years later.
Langstrom first clashes with the Batman when he tries to steal the chemicals needed to reverse his transformation, but his control over the new animalistic instincts resulting from his bat-like state is tenuous, and Batman is forced to subdue him in order to administer the antidote.
Dr. Langstrom later refines his serum, enabling him to retain his human intelligence while in bat form, and allowing himself control over his transformations. He works for a time as a detective and independent crime fighter as Man-Bat, marries and has a daughter. Eventually his instability returns and he is left unable to control his transformations. In this condition, he again clashes with Batman in the Batcave (which he finds by following other bats through the network of caverns; although he does not recall its location while in human form, and he never discovers Batman's secret identity), believing — erroneously — that his daughter is dead and that Batman is somehow responsible.