Who is Fortinbras? What is his role in the play?

Fortinbras

The Prince of Norway. In many ways his story is parallel to Hamlet's: he too has lost his father by violence (Old Hamlet killed Old Fortinbras in single combat); he too is impeded from ascending the throne by an interfering uncle. But despite their biographical similarities, Fortinbras and Hamlet are constitutional opposites. Where Hamlet is pensive and mercurial, Fortinbras is all action. He leads an army through Denmark in order to attack disputed territory in Poland. At the end of the play, and with Hamlet's dying assent, Fortinbras assumes the crown of Denmark.