Blunt is a loyal nobleman. He's a messenger for the king and conveys important news throughout the play. He's by no means a major character, but we think he's a significant figure nonetheless. During the battle at Shrewsbury, Blunt – one of many soldiers dressed in the king's coats – is killed by Douglas, who mistakes him for King Henry. When Douglas later encounters the real King Henry on the battlefield, he says he fears Henry is just another "counterfeit."
Blunt's very convincing costume, then, suggests that just about anyone can play the role of a king, as long as they have the right wardrobe. This recalls another significant scene in the play where Prince Hal and Falstaff take turns playing "King Henry" during their impromptu skit at the Boar's Head Tavern. Why does any of this matter? Well, it suggests that kingship is merely a "role" to be played, which is a pretty rebellious attitude for the play to take considering the fact that kingship was thought to be divinely ordained. For more on this, check out our discussion of play-acting and theater in "Art and Culture."