Some images perfectly capture the moment they were taken; this is one. Eisenstadt snapped these three at a party in Berlin in 1929, when the most famous of them was the woman in the middle: Anna May Wong.
On the left, of course is Dietrich, who by that point had been toiling away for the better of a decade without becoming much more than a slightly risqué leading lady on stage and in unimportant films, a bit of a show-off and a climber. On the right is Leni Riefenstahl, at that point a rising star still four years from finding her niche as the Nazis' cinema darling.
Wong, though, at 24 here, had been a star since her mid-teens, with 30 Hollywood pictures and a handful of European hits behind her. She was a star in cabaret as well, singing wry songs like Noël Coward's "Half-Caste Woman" and showing off her perfect figure in clinging lamé gowns. Talkies kind of did her in, though, forcing her back to Los Angeles and the sort of supporting parts open to even the most beautiful Asian woman in the world.
If you want to know how the story turns out, Richard Corliss wrote an excellent multi-part feature a couple of years ago in Time. It's worth a read.