This film was made during that brief postwar period when people had more important things to worry about than film censorship. It dealt with Paragraph 175, the law which criminalized male homosexuality. Veidt plays a homosexual -- said to be the first openly homosexual character in film -- who's arrested under the law and ends up committing suicide. (Spoiler.)
Even his father says that suicide would be the honorable thing for him to do. Naturally this reminds me of the recent suicide of transgender teen Leelah Alcorn. Here we are a century later.
Well. Conrad Veidt. He's best known for playing the lead Nazi in Casablanca. In fact he was one of the many people who found it expedient to leave Nazi Germany. One of the stories told about him is that when the Nazis required people to provide their ethnic background on job applications, he always wrote Jude even though he was not Jewish. And then there's the "playing gay" thing.
I liked the film though. Just wanted to mention that although Hirschfeld subscribed to the then-popular belief that lesbians and gay men constituted a "third sex" and that they were all, in effect, transgender (being "male people in female bodies" or "female people in male bodies,") the sexologist does point out that in fact not all gay men are effeminate and not all feminine men are gay. It's a distinction that often gets overlooked when discussing the late 19th and early 20th century theories around gender and sexual orientation.