Huan

A Noble Hound From Valinor, Huan was originally one of the immortal hunting dogs of Oromë, the Huntsman of the Valar. When he followed his first master, the Noldorin Elf Celegorm, away from Valinor, he became mortal, but it was decreed by the Valar that he would only die at the jaws of the mightiest Wolf of Arda. Huan was more intelligent than any other hound since seen in Middle-earth; he could even speak with words upon occasion, as well as being exceptionally eloquent in the usual houndish vocabulary of gestures and postures. He betrayed his treacherous master to aid Lúthien and later Beren in the Quest of the Silmaril. In this he met his doom; after killing numerous werewolves and defeating Sauron when the evil Maia took wolf- form, Huan both slew and was slain by Carcharoth, the huge wolf bred by Morgoth to be the noble Hound's bane.