My favorite Batman is one that most don't usually think about when they talk about the caped crusader: Dr. Kirk Langstrom AKA Man-Bat. Like Batman's polar opposite, he represents what Bruce Wayne doesn't want to happen; he does not want the bat to overshadow the man. Plus, his backstory is both intriguing and tragic.
Dr. Kirk Langstrom was a scientist who worked in the field of bats with his wife, Francine. Over the years, Langstrom noticed that he was going deaf. In an effort to save his hearing, he spliced his DNA with that of a vampire bat. This resulted in his transformation into Man-Bat. However, the transformation and his loss of control caused him to accidentally kill his wife in the process.
He's such an interesting and unique villain that I think should get more praise and recognition especially in the newer Batman comics and other properties. Perhaps a nod to him in the hit Gotham TV show. Nonetheless, Man-Bat will remain my all-time favorite Batman villain.