A major character in Tolkien's book The Silmarillion, Glaurung was the first and one of the greatest of the Uruloki. Although without wings, he could breathe fire and cause hypnosis and was a formidable adversary. He played a crucial role in Nirnaeth Arnoediad in routing the elven armies, and later led orkish forces in attacks in Beleriand.
As the forces of Nargothrond, inspired by Turin, became increasingly assertive, Glaurung launched an attack on the previously hidden city, using a bridge built to enable the city's elves to go to war. He routed and burned the city, slaying many of its defenders, including Gwindor.
He hypnotised Turin, sending him on a wild goose chase to Mithrim, and later Nienor, who developed complete amnesia as a result (hence her marriage to her brother Turin).
Slain by Turin as he came forth against a host from Brethil. Turin attacked his vulnerable underside, mortally wounding the dragon.
He's usually depicted in pictures as a huge green worm-like dragon.