The Dark Avenger was a baseline costumed hero active in New York during the late 1920s and most of the 30s. At that time the New York Police Department denied his existence, claiming him to be an urban legend or newspaper hoax. He was the inspiration for other mystery men as well as fictional heroes such as Batman or the Shadow.
He's known to take over people's identities. At various times, he's been Reed deBritt, the publisher of the New York Clarion, and the Special Agent in charge of the Washington office of the FBI. Whether he's still alive is unknown at this time, since Mephisto has a major grudge against him.