Rolf Gruber is a character in "The Sound of Music". He's the young messenger boy who's in love with the oldsest von Trapp kid, Liesl--they're the ones who sing "Sixteen Going on Seventeen" together. Unfortunately he falls to the dark side--as in Nazis--and winds up breaking up with Liesl and (in the Julie Andrews movie version) turns the rest of her family in. He keeps quiet in the play (still unable to put Liesl in any real danger.) While the story was loosely based off real people, I doubt there was a real Rolf Gruber (feel free to correct me!) although I can't be the only one who thinks of him whenever they hear "Rolf". :)
In the Harry Potter series, Newt Scamander (the author of Fantastic Beasts and Where to Find Them) has a grandson named Rolf who later marries Luna Lovegood. They have twin sons Lorcan and Lysander.
Perhaps the most famous bearers of the name in modern times is Rolf Harris (born 30 March 1930), Australian musician, artist, children's entertainer and television presenter. He is most famous for his hits 'Tie Me Kangaroo Down, Sport' and 'Two Little Boys', as well as inventing the wobbleboard.