He played the part of the Nazi that is shot in the film Casablanca!
Werner Klemperer, known forever as Colonel Klink in Hogan's Heroes, refused that role until the producers agreed to rewrite it so that he was a bumbling fool who never succeeded at anything. He once said, "I had one qualification when I took the job: if they ever wrote a segment whereby Colonel Klink would come out the hero, I would leave the show." His father was Jewish, and his family left Germany in 1935 before it was too late.
Conrad Veidt was a very popular German actor in the 1920s to early 30s. In 1933, Goebbels was purging all Jewish actors from film & stage. Veidt had just re-married, to a Hungarian Jew. He was told by Goebbels' minions that if he divorced her and declared support for the Nazi regime, he could continue acting. His reaction was to fill in the "Race?" question with "Jude" in the questionnaire sent to all actors, though he himself wasn't Jewish, but rather was demonstrating his solidarity with his wife (like the non-Jewish Danes who put on the yellow star). Immediately after, they emigrated to the UK before Goebbels could arrest them.
After 8 years of starring in anti-Nazi movies, he & his wife moved to Hollywood for the express purpose of making movies that would help convince Americans to support the British war effort. Similar to Klemperer, he had his contract mandate that he would only play German characters if they were villains.
BTW, Hogan's Heroes Trivia: The actor who played Corporal LeBeau is a French Jew who spent 3 years in Buchenwald, and still has the tattoo on his arm today. 12 other family members went to Auschwitz and none came back. The only thing that saved him was his ability at the age of 16 to sing & dance and entertain the SS soldiers at the camp.