Nine Ringwraiths

Sauron's plans to enslave the Elves to his will failed when they became aware of his Great Ring, but in the War of the Elves and Sauron he was able to recover many of the Rings of Power from Eregion. He used sixteen of these to ensnare mortal races of Arda, and the greater part of these he assigned to Men, who had always fallen most easily under the power of the Dark Lords. So, he granted nine Rings of Power to nine lords of Men, each of whom slowly fell under his power until they became wraiths, dominated by Sauron's will and slaves to his One Ring. By the end of the Second Age, these had become the greatest and most terrible of all his servants, and they haunted Middle-earth until the time of the War of the Ring at the end of the Third Age.