Conrad Veidt as Major Strasser — It has been reported, though not verified, that Veidt identified himself as Jewish on Nazi questionnaires as an act of protest.
Veidt's wife was Jewish and Veidt himself was a target due to, among other things, performing in a pro-gay rights film in the 1920s. He donated a large amount of his personal fortune, and a fair chunk of his paycheck from this movie, to the English war effort.
Ironically all of the German actors in the film were Jews or German expatriates who fled the country when the Nazis took over, only to play Nazis in Hollywood. which most of them (Veidt in particular) were pleased to do, seeing it as a form of resistance by telling the world what the Nazis were like.