Thuringwethil

Sauron's messenger

Thuringwethil is the only vampire named in the histories. She served Sauron in the days when he held Tol Sirion as the Isle of Werewolves, and she carried his messages north to Angband and back. She went in the form of a great bat, and her wings were fitted at each joint with a claw of iron. Her name means Woman of Secret Shadow, and it suits what little is told of her: she is never seen in the tale except through her empty skin.

The bat-fell

When Lúthien and Huan overthrew Sauron in F.A. 465 and the tower of the isle was thrown down, Thuringwethil's winged fell was found among the spoils. Whether she perished in the fall of the tower or fled bodiless, as Sauron did in vampire shape when he abandoned his own form, is not said. Huan took the fell with the pelt of Draugluin and brought both to Beren and Lúthien in the woods near Doriath.

Lúthien put on the bat-skin, and with the werewolf-shaped Beren beside her crossed Anfauglith to the gate of Angband. Carcharoth was not deceived, but the disguise had brought them to the threshold, and Lúthien's own power carried them past. In this way the messenger of Sauron unknowingly carried the thief of the Silmaril into her master's stronghold.

Nature

The vampires of Angband are best understood as fallen spirits in bat-form, since Sauron himself assumed that shape when he fled from Huan. Thuringwethil, then, was probably a lesser spirit of the same order, bound to the shadow and to the winged shape she wore.

Not told. Her winged skin was found in the ruin of Tol Sirion after Sauron's defeat, F.A. 465, and later worn by Lúthien.