Locastro

Sealed within this prison is the creature known as Locastro; woe be to those who enter, and unleash his evil upon the world once more.
-The Ancient Draconic inscription outside the entrance to Locastro's tomb, hidden somewhere deep within Northguard.

Summary

During the time of The Old World, when behemoths roamed Kermoria, the giants of Northguard were already an ancient and learned species.  Unlike much of the rest of the world, Northguard was generally too cold for the behemoths to survive, and so it was generally considered a 'safe' place to exist.  

Amongst the Storm Giants, one chieftain, who's savagery was legend, rose amongst the rest, unifying their clans beneath a single, barbaric banner; Locastro.

Locastro was a man of singular fury, destroying anything and everything (and everyone) who stood in his way; he felt that unifying not only the Storm Giants, but all Giants of the Ordning, under his banner, was the only way forward for their species.

Along with his three greatest Chieftains, two men and a woman known as Taylern, Ky'len and Rey, they sowed terror and chaos across Northguard for many years.

Soon, the clans were brought to heel, but still, Locastro wanted more.  His desire for power overtook him, and he made a terrible pact with a being of great power (some legends state a demon, others a dragon, some even so far as to say one of the behemoths), a pact which stripped him of what little restraint remained within him and let loose his inner animal.

And thus, as many tribal legends amongst Pantheons and Deities of the Old World state, Lycanthropy was born into Kermoria, with Locastro as it's father.

For years, Locastro and his minions preyed on the countryside, killing, maiming and slaughtering anyone who stood in their way.  Eventually, using ingenuity of the Dwarves of Karak Hungren, the Elves of Frostberg and the combined might of many giant tribes, along with the powerful magics of Thunder Gulch and it's Tempest Obelisk, managed to imprison Locastro within an underground temple, hidden deep within a mountainside.

The door to that temple was then sealed with powerful magics and runic wards, (hopefully) preventing him from ever being awoken.  His lieutenants were buried with him, each of their souls (and his) bound to a sacred, rune-scribed object.  With all the objects together, and their words of power spoken, the souls of those beasts were bound eternally to their rest.