Who is Sauron from Unfinished Tales of Numenor and Middle-earth and what is their importance?

The dark lord as he is otherwise know, Sauron is the greatest servant of Melkor, and the scourge of Middle Earth. It is Sauron's wish to hold all of Middle Earth in thrall to him, and it is the goal of all free races to destroy him forever. He is the one who has the rings of power created in the first place, and he binds the Ring of Power to his very soul. It is because of this that Sauron cannot be completely destroyed while the ring still exists.