Nazgûl

The Ringwraiths, (or Black Riders, or Nazgul) of The Lord of the Rings were ghostly spectres sent by Sauron to recover the Ring from Baggins of the Shire. The greatest weapon of these horsemen was not swords but sorcery and fear.

After annoying Farmer Maggot, terrifying Sam's father, and nearly killing Fatty Bolger, some of them pursued Frodo and his three hobbit friends to the Brandywine, where they barely escaped by ferry. Several attacked Strider and the four hobbits in Bree and at Weathertop. In a dramatic confrontation at the ford of Rivendell, they were unseated and apparently drowned by Gandalf. However, only their horses drowned, and Sauron gave them new steeds, flying monsters with great leathery wings.

The Nazgul were originally nine kings of men who were corrupted by rings of power.