"Those who used the Nine Rings became mighty in their day, kings, sorcerers, and warriors of old. They obtained glory and great wealth, yet it turned to their undoing. They had, as it seemed, unending life, yet life became unendurable to them. They could walk, if they would, unseen by all eyes in this world beneath the sun, and they could see things in worlds invisible to mortal men; but too often they beheld only the phantoms and delusions of Sauron. And one by one, sooner or later, according to their native strength and to the good or evil of their wills in the beginning, they fell under the thralldom of the ring that they bore and of the domination of the One which was Sauron's. And they became forever invisible save to him that wore the Ruling Ring, and they entered into the realm of shadows. The Nazgūl were they, the Ringwraiths, the Enemy's most terrible servants; darkness went with them, and they cried with the voices of death"
-The Silmarillion: "Of the Rings of Power and the Third Age", 346
Third time as MOTD ... what an odd system of picking. There are people who make things so much more complex and interesting than this little guy. Guess I shouldn't complain at the honor though, so cheers.