Who are the Black Riders from 'The Lord of the Rings'?

"...Nine for mortal men doomed to die..." The Black Riders, or Ringwraiths/Nazgul in The Lord of the Rings were "great kings of men" in Middle-earth that came under Sauron's sway. Enticed by the promise of immortality, the kings eagerly accepted the Rings offered to them by Sauron, and, for a time, enjoyed seemingly everlasting life and power. Gradually, however, as their lives were stretched to far beyond their given limit, they entered into a state of "undeadness," and hated the light. The Nine rings bound them to Sauron, and they became his greatest and most feared servants. Their greatest weapon was the terror and despair they inspired in the hearts of men. Their chief was the Witch King of Angmar; a great and evil sorcerer. The Ringwraiths were destroyed when the One Ring was cast into the fires of Mount Doom.