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, starring in a pro-gay rights film in 1919. If you read Strasser as Armored Closet Gay, that might be because Veit was bisexual himself, yet another reason for the Nazis to hate his guts. There were rants in Nazi papers at the time claiming that because of the aforementioned gay rights movie and his other human rights films (including ones clamoring for women's reproductive rights), he was responsible for making young Germans boys and girls homosexual and promiscuous. A lifelong supporter of human rights and liberal causes, he donated a large amount of his personal fortune, and a fair chunk of his paycheck from this movie to the English war effort.
Oh, and he helped Paul Henreid help escape Europe. The Austrian Henreid arrived in Britain just after war had been declared and was therefore an enemy alien, whereas Veidt had become a British citizen in 1939. Veidt sheltered Henreid at his own house and vouched for Henreid to the British authorities, so that Henreid could stay in the UK until Veidt had scraped up the money for Henreid to cross the Atlantic.
Ironically, all of the German actors in the film were either 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.
Serendipity Writes the Plot: Everybody Comes to Ricks, the unproduced stage play that this movie was based on, ended with Rick and Ilsa running away together to America; the movie only got its iconic Bittersweet Ending because the Hays Code forbade movies from showing characters getting away with adultery.
What Could Have Been: The iconic La Marsaillaise sequence was intended to been even more pointed against the Nazis. The original song Major Strasser and the other Germans were to sing was not Die Wacht am Rhein, a WWI marching song, but instead Das Horst-Wessel-Lied, the Nazi Party anthem and unofficial second national anthem of Nazi Germany. However, Warner Brothers changed it when they realized that the song was under copyright, which wouldn't have been a problem if the film were only being distributed in Allied territory. However as the film was also going to be released in neutral countries as well, it could have caused major diplomatic headaches and even opened Warner Brothers to the absurd possibility of being sued by the Nazis for copyright infringement.