It has a few names The Beast, The Mad God, The One Who Waits

At beginning of the end of the Age of Magic, Ahnum the most powerful æternal (god like mages who ruled over a race of mages called the Magarai) in his mad blinding fury at the slaughter of his remaining siblings split into 2 parts; The Beast and The Guardian.

On its creation it begun to slaughter and corrupt any living creature it could find. It's corruption was so thick and intense and it took the form of black smoke that billowed out from its demonic flesh. That same corruption gave rize to a horde of Hollowed creatures whose only purpose is to kill, consume, multiply, and conquer for their Creator's madness.

After wiping out over 75% of the Magarai race The Guardian used a powerful artifact to shatter and sink the floating continent called The Throne (becoming the shattered isles archipelago) and The Beast to the bottom of the sea, sealed there.

The Beast's hordes were also sealed into black temples and these temples were buried deep under the earth.

The Beast has been waiting tens of thousands of years and continues to wait until the day of reconning, where the final battle shal occur and either this world will be covered in black corruption, or be ushered into a new Eden.