Greatest of the wolves or "werewolves" of Morgoth/Sauron in Tolkien's book The Silmarillion. Fathered by Draugluin, Carcharoth was specially trained and fed up to be the most powerful wolf ever, because of a prophecy that Huan the wolfhound could only be killed by the greatest wolf in history.
Carcharoth was posted outside the fortress of Angband to protect Sauron from any attempt by Beren, Luthien and Huan to obtain a Silmaril (in fulfilment of their oath to Elwe). Put under a sleep spell by Luthien, he failed to prevent the theft of a Silmaril, but he attacked Beren when he tried to leave the tower, biting off the hand containing the Silmaril.
Tormented by its light which he found unbearable, Carcharoth then ran rampage across Beleriand until hunted down and slain by Huan. As the prophecy foretold, Huan was also slain in this combat.
Carcharoth is depicted on the cover of the book The Lays of Beleriand as a gigantic slavering wolf with dark fur and red eyes, belching smoke.