The movie that turned Marlene Dietrich into an icon in the early 1930's, and marked the beginning of her famous 7-film collaboration with Josef Von Sternberg. This is a very dark, almost disturbing story of a pathetic old man (Emil Jannings) who becomes the cuckold of the cool, calm, preternaturally collected Dietrich. The way director Sternberg shot and lit Marlene Dietrich became the stuff of Hollywood legend and it all starts here. It's a great movie, and if I were you I'd be sure to watch it in its original German (although they did shoot two versions, with one in English).
The only trailer for this movie is without subtitles, so instead here's the famous scene (in English) of Marlene waltzing into movie history by singing "Falling in Love Again."