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[LotR] Who exactly IS the Mouth of Sauron?

For those who don't know, he is the handsome man with slits in his mouth when Aragorn & Co. approach the Black Gate in the extended version.
gpt
He is a Black Numenorean, of the same race as Aragorn, only he is in the service of Sauron.  Back when Numenor was at it's peak of power they invaded Middle Earth to defeat Sauron.  The armies of Numenor were so vast and powerful that Sauron's armies literally fled, leaving Sauron at the mercy of the men of Numenor.  They took him back to their home as a captive where he quickly spread his influence, lies and his wickeness amongst the men of the island.  Two camps arose, the Elf-Friends, from whom Aragorn is descended, ad the King's men, who were won over by the lies of Sauron.

Sauron influenced the Numenoreans to invade Valinor and wrestle immortality from the Elves and Ainur.  A foolish plan as the land did not grant immortality, it was just inhabited by the immortal.  Those few Numenoreans who refused to sail for Aman/Valinor, instead sailed for Middle Earth.  The armies of Numenor landed on the shores of Aman, Eru Illuvatar/God himself cast the armies into a cave for eternity and sank their island home. (The Ainur could do nothing as they had no authority over the race of Men, only God can punish them.)  

The Elf-friends landed in Middle Earth, founded Arnor and Gondor, but also found that some Numenoreans who were still loyal to Sauron inhabited the land in various places.  These Black Numenoreans served Sauron for centuries upon centuries.  Their numbers are not known.  The Mouth of Sauron's true name is not known, even he has probably forgotten it due to the madness of Sauron's influence.