Man-Bat was a creature created by Langstrom through splicing and an enemy of Batman.
Dr. Kirk Langstrom was a biologist specializing in bats. He had hoped to extract bat DNA to give human beings sonar as a cure for deafness. When he tested the serum on himself it did cure his deafness but it also turned him into a human/bat hybrid. Losing his basic human senses he went on a rampage in Gotham until stopped by Batman. Coming to like the power of his Man-Bat form. He took the serum again and gave some to his wife Francine Lagstrom, turning her into She-Bat. They attack Gotham together but were again stopped by Batman. However he does not seem to do intentional evil, because on occasion when he maintains his intelligence in his Man-Bat form he has done good. Examples include helping detective Jason Bard, and once helped Superman overcome kryptonite poisoning. Kirk and Francine had two children named Becky and Aaron. Aaron was born in a Man-Bat form due to lasting effects on Kirk and Francine's DNA.
Batman the Animated Series
Man-Bat appears in Batman the Animated Series as a zoologist at Gotham City Zoo. Dr. Langstrom had hoped to mix human and animal DNA to creat a new species. However he could not control himself in this form and he went on a rampage, (which Batman was blamed for due to a similar appearance). Man-Bat was stopped and eventually cured. However his wife Francine was unwillingly exposed to the formula in another episode and transformed into She-bat. Dr. Langstrom and Batman worked together to return her to normal.
Professor Milo later used Dr. Langstrom's research for his work at Project Cadmus.
Man-Bat also appears in The Batman as a more villainous character. In this version, Dr. Langstrom worked for Wayne Enterprises and had an obsession with Batman. Disguising his research as a cure for deafness, he was actually preparing a serum to give him bat powers. Batman managed to defeat him and he was sent to Arkham. Later in the series Penguin used a sonar device to mentally control Langstrom in his Man-Bat form to commit robberies for him. Batman managed to stop them both. Eventually Langstrom renounced his criminal ways and helped Batman defeat the Terrible Trio, who had stolen mutagen from Langstrom to get powers of their own.
Beware The Batman
Man-Bat appears in the episode "Doppelganger" where Kirk Langstrom is working on a cure for diseases using bat DNA however Professor Pyg and Mr. Toad (DC) use the DNA on him which turns him into Man-Bat. They then use a drugged collar to control him and he goes on a rampage throughout Gotham. Batman subdues him and removes them collar which frees him. Langstrom then tells Batman and Katana how Pyg and Toad plan to use his work to create an army of hybrid creatures. The three of them head to Pyg's hideout and free their hostages. While Batman fought Pyg, Katana and Man-Bat fought Toad who was able to reattach the collar to Man-Bat. Toad uses him to capture Katana and attack Batman. He and Batman fight each other until Batman is able to pry off the collar and the two of them catch Pyg and Toad who are later arrested. Batman then convicnes Langstrom to continue his research to help him and other people. Langstrom accepts and leaves Batman before he could be seen by the police.