(g hard). The name of Llewellyn's dog. One day a wolf entered the room where the infant son of the Welsh prince was asleep; Gelert flew at it and killed it; but when Llewellyn returned home and saw his dog's mouth bloody, he hastily concluded that it had killed his child, and thrust it through with his sword. The howl of the dog awoke the child, and the prince saw too late his fatal rashness. Beth-gelert is the name of the place where the dog was buried. (See Beth-Gelert, Dog.)
A similar story is told of Czar Piras of Russia. In the Gesta Romanorum the story is told of Folliculus, a knight, but instead of a serpent the dog is said to have killed a wolf. The story occurs again in the Seven Wise Maste,s. In the Sanskrit version the dog is called an ichneumon and the wolf a “black snake.” In the Hitopadesa (iv, 3) the dog is an otter; in the Arabic a weasel; in the Mongolian a pole-cat; in the Persian a cat, etc.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894