Nazgul

The  Nazgûl (from Black Speech  nazg, "ring", and  gûl, "wraith, spirit" (presumably related to  gul, "sorcery"); also called  Ringwraiths,  the  Nine Riders, or simply  the Nine are evil supernatural beings of Middle-Earth . They were once human men  who were succumbed to nine rings of power; which made them great kings  and attained near-immortality as  wraiths, unfortunetly they became servants of the dark lord, Sauron; bound to the power of the One Ring.  The  Nazgûl are Sauron's "most terrible servants".

They sometimes venture on horseback, or even take flight on their fell beasts, on certain agendas; even joining in with the wizard, Saruman.

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