The Nazgûl, Ringwraiths or Úlairi are servants of Sauron. They were human kings and leaders in the Second Age. Sauron gave to them nine of the Rings of Power. With time they became like undead ghosts. They are invisible, but their eyes can sometimes be seen as a red light. They wear black cloaks, and usually ride black horses. Later in the "Lord of the Rings" they ride winged creatures called "fell beasts". When riding a fell beast they are also called "Winged Nazgûl".