§ Of Beren and Lúthien The Silmarillion

It chanced that Celegorm and Curufin went on a hunt through the Guarded Plain; and this they did because Sauron, being filled with suspicion, sent forth many wolves into the Elf-lands. Therefore they took their hounds and rode forth; and they thought that ere they returned they might also hear tidings concerning King Felagund. Now the chief of the wolf hounds that followed Celegorm was named Huan. He was not born in Middle-earth, but came from the Blessed Realm; for Oromë had given him to Celegorm long ago in Valinor, and there he had followed the horn of his master, before evil came. Huan followed Celegorm into exile, and was faithful; and thus he too came under the doom of woe set upon the Noldor, and it was decreed that he should meet death, but not until he encountered the mightiest wolf that would ever walk the world.