Rudolf Klein-Rogge was a German stage and film actor of the 1920s and 30s. He is best known for his roles as the mad scientist Rotwang in Fritz Lang's film "Metropolis", and as the title character in Lang's Dr. Mabuse series. Wikipedia
The definitive Wikipedia entry for Rudolf Klein-Rogge. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Rudolf_Klein-Rogge