Draugluin was the very first Werewolf in Middle-Earth, and was first mentioned in The Silmarillion. Like his fellow Werewolves, he was a servant of Morgoth and Sauron.
Draugluin was bred from wolves, but became something more sinister after Morgoth personally sent an evil spirit into him to corrupt him. From there, Draugluin would go on to sire all of the Werewolves in Beleriand. He dwelled with Sauron in Tol-in-Gaurhoth.
In the year FA 465, he was killed by Huan, the great hound of Celegorm, but not before informing his master Sauron that Huan was present. Afterwards, Luthien and Beren used his pelt to sneak into Angband.
As the original Werewolf in Tolkein's legendarium and the one from whom the others first came, he is essentially to Werewolves what Glaurung is to Dragons and Ungoliant to Great Spiders.