Who is a foil to Hamlet?

That would be Young Fortinbras. Hamlet is impressed that Fortinbras is such a "he man" ready to risk lives simply for a fight. He wishes he wasn't such a coward over something that has really insulted him. Hamlet resolves to be a "tough man" just like his hero Fortinbras. Hamlet launches into a self deprecating rant about how much of a coward he is. He is impressed by Fortinbra's aggression over a "straw" and laments his own inaction over feeling personally used and insulted.