The Beast of Beldra is thought to have been a massive dog that shared certain characteristics of a bull. The monster may have shared its name with Beldric the Enchanter, the person who tried to unleash it on the world while he was working the Fields of Frotzen (sometime shortly before or at the start of the Great Monster Uprising) but was stopped by Bozbik the Face Breaker.

Some believe that the Beast might somehow be a personification of the Enchanter's own devious nature, or that it might have been a creature that had ties into his own family history, but the name similiarities might just as easily have been a coincidence.

SOURCE(S): Legends of Zork (game, personal correspondence from the author of 'Enter the Face Breaker' quest)