Who is the Porter in Macbeth?

The Porter is a minor character in "Macbeth" who serves as the doorkeeper at Macbeth's castle.  Immediately after the murder of King Duncan, the Porter appears in response to the knock at the gate.  He is still drunk from the festivities of the night before, and he serves as a humorous break in the play from the tension and gory bloodshed the murder of Duncan produced.  He pretends to be the gatekeeper of Hell in his drunken state, which is not too far from the truth since Macbeth and his wife should have been excellent hosts instead of heartless murderers.  This parallism of Macbeth's castle with Hell also underlines the fact that Macbeth has just lost his soul in murdering his King and cousin.