Thuringwethil
From the One Wiki to Rule Them All, the Lord of the Rings Encyclopedia.
Thuringwethil was a vampire servant of Sauron, during his time serving Morgoth. She served as a herald for Sauron and "was wont to fly in vampire's form to Angband; and her great fingered wings were barbed at each joint's end with an iron claw." -The Silmarillion: Of Beren And Luthien
Additionally, Luthien disguised herself as Thuringwethil in order to infiltrate Angband. She cast off the disguise, however, at the entrance to Angband.
