In J. R. R. Tolkien's universe of Middle-earth, the Mouth of Sauron was the dark lord Sauron's servant and representative.
He was one of the Black Númenóreans, and briefly appeared in person when he haggled with the army of the west in front of the Morannon, trying to convince Aragorn and Gandalf to give up and let Sauron win the battle for Middle-earth. When Gandalf turned his proposal down, the mouth of Sauron set all the armies of Barad-dûr on to them.
Also known as the Lieutenant of Barad-dûr, he had served Sauron all his life, and had forgotten his own name. A man of great stature, he was potentially the equal of the Dúnedain, but had fallen into darkness.
A tall and evil shape, mounted upon a black horse… The rider was robed all in black, and black was his lofty helm; yet this was no Ringwraith but a living man. — The Return of the King.
In the movie by Peter Jackson, the Mouth of Sauron does not appear in the theatrical cut of ROTK, but screenshots released over the net reveal that he does appear in the extended version.
