Dr. Dahm, known as Dr. Zero in Japan, is a character from Streets of Rage 3.
Dr. Dahm is a mad scientist working for the Syndicate Crime Organization. While in the Japanese version of the game he doesn't have much of a role, only showing up before the final boss and never being mentioned, in the American version his role is greatly expanded, where he is responsible for creating all of the robot clones being used by the Syndicate. In the American ending it is also revealed he was aprehended by the police and sent to a asylum.
While he isn't confronted directly the player must fight a mechanical arm controlled by him as a mini-boss. It is fought over a moving conveyor belt which pulls the player into a electrified field on the back, forcing the player to move down constantly while avoiding the arm's attacks and hitting it as well.