Real name: (see comments)
First Appearance: Detective Comics I#31 (September 1939)
Weapons: vampires and werewolves
Quotes: "Soon your Julie will be as we are..."
Worst Act: Being a vampire and werewolf
Created by: Gardner Fox (writer) and Bob Kane (artist-credited)
Now here we have an unusual rogue. The Monk is somehow both a vampire and a werewolf, plus his story is the first proper two part story. Kidnapping Julie Madison (Bruce Wayne's rarely mentioned fiancé), with the intent to turn her into a werewolf, the Monk and his assistant Dala were also the first foes properly killed by Batman too. Silver bullets to the head no less.
That would be the last appearance until 1982 when Gerry Conway brought the Monk and Dala back, this time with the origin of being Louis DuBois and his sister Dala. Cruel plantation owners who were cursed by their abused former slaves shortly after the Civil War, the story was basically an Earth-1 update of the first story.
Matt Wagner brought the Monk back for his wonderful Batman and the Mad Monk miniseries, which was basically another update on the story. Worth the effort to read for sure. Wagner added another take on the character, this time a bit more vague. Is his an actual vampire or a former son of Gotham turned cult leader? The story doesn't say one way or another.