At its head there rode a tall and evil shape, mounted upon a black horse, if horse it was; for it was huge and hideous, and its face was a frightful mask, more like a skull than a living head, and in the sockets of its eyes and in its nostrils there burned a flame. The rider was robed all in black, and black was his lofty helm; yet this was no Ringwraith but a living man. The Lieutenant of the Tower of Barad-dûr he was, and his name is remembered in no tale; for he himself had forgotten it, and he said: ‘I am the Mouth of Sauron.’ But it is told that he was a renegade, who came of the race of those that are named the Black Númenóreans; for they established their dwellings in Middle-earth during the years of Sauron’s domination, and they worshipped him, being enamoured of evil knowledge. And he entered the service of the Dark Tower when it first rose again, and because of his cunning he grew ever higher in the Lord’s favour; and he learned great sorcery, and knew much of the mind of Sauron; and he was more cruel than any orc.He it was that now rode out, and with him came only a small company of black-harnessed soldiery, and a single banner, black but bearing on it in red the Evil Eye.
...
‘These are the terms,’ said the Messenger, and smiled as he eyed them one by one. ‘The rabble of Gondor and its deluded allies shall withdraw at once beyond the Anduin, first taking oaths never again to assail Sauron the Great in arms, open or secret. All lands east of Anduin shall be Sauron’s for ever, solely. West of the Anduin as far as the Misty Mountains and the Gap of Rohan shall be tributary to Mordor, and men there shall bear no weapons, but shall have leave to govern their own affairs. But they shall help to rebuild Isengard which they have wantonly destroyed, and that shall be Sauron’s, and there his lieutenant shall dwell: not Saruman, but one more worthy of trust.’
Looking in the Messenger’s eyes they read his thought. He was to be that lieutenant, and gather all that remained of the West under his sway; he would be their tyrant and they his slaves.