Thuringwethil
the vampire; the fell spirit of the Enemy
Name and Being
Thuringwethil — “the vampire” — is one of the fell spirits of Angband, a shape-changer (like the werewolves and vampires of the Enemy’s host), in her usual form “a great bat” — she was a messenger and (with Draugluin) one of Sauron’s dark agents, her name, “the shadow of night” — is among the few named beasts of the shadow beyond the wolves.
The Flight into the Bat
In the tale of the Isle of Werewolves: after Huan had overthrown the werewolves and the wolf-lord Draugluin, Sauron fled from within his tower in the shape of a great vampire (the form of Thuringwethil, or his own bat-shape), and escaped the hound’s final stroke — flying away to Taur-nu-Fuin. (In some accounts, Lúthien made use of Thuringwethil’s cloak, or her form, to enter the isle.)
Significance
Thuringwethil is the “vampire” of the Enemy’s menagerie — the bat-shape of the dark flight (and the byword for Sauron’s escape); her name gives the kind of the “vampires” of the First Age (the malevolent flying spirits, kin to the werewolves), and she is often invoked in the tradition of Lúthien’s disguise.