Ringwraiths

The Ringwraiths were, originally, nine great Kings of the human kind, who were corrupted by the power that Sauron gave them by handing them the Nine Rings. They turned invisible to everyone except the bearer of the One Ring and became slaves, following every dark order that their Master gave them. To have a shape visible to others, they wore mails of silver and long, black, hooded cloaks. They all carried blades made of black metal, that when stabbing someone would leave a piece of it inside of that person. That small piece would gnaw its way to the person's heart and once there, it would turn him or her into a wraith, to serve under the Nine for all time. The most skilled healers of the Elven kind were able to stop the poisoning and remove the piece of the blade, but the wound would always be there and would send out waves of pain if the one carrying the blade itself was near.

The Ringwraiths were originally destroyed when Frodo Baggins destroyed the One Ring in the book War of Magic, but through Saruman's magic they were revived to serve under him. This was something that the members of the Alliance had not known about and thus, they were attacked unexpectantly somewhat west of Rivendell (in the book For the Magic Realm). Several of the members were stabbed, among them Freedom, Sarah Ferenish, Albus Dumbledore and Edmund of Narnia. They were saved by the Riders of Rivendell and later cured by Elrond.

These wraiths disappeared when Saruman was destroyed, but they once again appeared when Sauron was resurrected. This time they managed to stab Frodo Baggins, the bearer of the One Ring, but also he was cured by Elrond.

The wraiths disappeared for all time when Frodo destroyed the second One Ring.