Awesome, Dear Boy: Jonah Hill made only $60,000 (the lowest possible SAG-AFTRA rate) on the film; he simply wanted the opportunity to work with Martin Scorsese.
Promoted Fanboy: Which could also make him this, since Hill had established as far back as in 2010 (well before he had even earned his first Oscar nomination) that Goodfellas was his favorite film of all time.
Fake American: The Australian Margot Robbie as Naomi (though Naomi is half British)
Fake Nationality: The French Jean Dujardin as a Swiss banker. Although considering that Switzerland is a multi-cultural nation with German, French, Austrian and Italian influences, it makes sense for a French man to pass as Swiss.
Star-Making Role: Not that she was entirely obscure beforehand, but Margot Robbie's profile was increased considerably by her appearance in this film, to the point where she was widely considered a serious candidate for the Best Supporting Actress category at the 2014 Oscars (though ultimately wasn't nominated).