Who are Rosencrantz and Guildenstern?

Rosencrantz and Guildenstern are friends of Hamlet's from the University of Wittenberg. Claudius invites them to court in order to spy on Hamlet. Rosencrantz and Guildenstern are often treated as comic relief; they are sycophantic, vaguely absurd fellows. After Hamlet kills Polonius, Rosencrantz and Guildenstern are assigned to accompany Hamlet to England. They carry a letter from Claudius asking the English king to kill Hamlet upon his arrival. Hamlet discovers this plot and alters the letter so that Rosencrantz and Guildenstern are put to death instead. We learn that they have indeed been executed at the very close of the play.