The Behemoth was a monster of the sea created by the Evil gods from the Original Clay to defile the realm of Hydana. A creature, known simply as "The Sea Monster" was often confused with the Behemoth as being one in the same. However, they were distinct beasts.
The Behemoth was one of the most powerful beasts of Evil during the First Battle and he is remembered in the constellation bearing his name in the Northern Skies of Titan. Although The Tale of the First Battle does describe the battle between Ichthys and the Behemoth, it is vague as to the fate of the Behemoth. Certainly it was severely injured in the struggle, but it swam away into the depths of the ocean before the chance to make certain of killing or banishing it was taken. To this day sailors tell stories of the Beast and of obscure sightings. If it did survive its injuries it may still be out there, somewhere.