Callieach

A fearsome race from the distant past. The Callieach eventually came into conflict with the Trow, and were destroyed in that conflict. In their final days, rather than be hunted to extinction by the Trow, they destroyed themselves and their hunters, leaving behind the Great Devoid. -Callieach Description, Glossary, Myth II Manual

Description
The Callieach were a race of powerful magic users during the Age of the Trow. Not much is known about the them, save for legends of their powerful magics and artifacts. While the Callieach were a frail race, their talent for magic was beyond anything that the wizards of the present day could achieve.

The Callieach were the first to uncover the secrets of dream magic from fragments of the Wyrd Runestones, changing the fabric of existence. With these Runestones, they were able to construct magical artifacts such as The Rod of The Callieach. They also created other devices that granted them abilities for shifting mountains, incinerating entire cities, and granting immortality. They built grand cities and became a powerful civilization, catching the attention of the Trow.

Wanting to harness the power to build more extravagant temples for themselves, the Trow attacked the Callieach cities and stole the Runestones from them, inciting a war between the two races. Unable to reason with the iron clad giants, the Callieach warned them of retaliation of their assaults did not cease. The Trow paid no heed, causing the Callieach to call upon their more powerful magic to sink Si'anwon beneath the Great Sea, taking the Runestones and the powers that they contained with it. The Trow were outraged that a "lesser race" dared to defy them.

Despite having god-like magic, the Callieach were no match for the might of the Trow and their iron weapons. They fled from their homes to escaped up into the mountains, with an army of iron clad giants in pursuit. Not wanting to be hunted down into extinction for their final stand, the last of the Callieach summoned the dream magic of Wyrd. A massive bottomless pit ripped beneath their feet, destroying themselves along with their Trow pursuers. This left behind the Great Devoid.

Their sacrifice soon showed that they had an indirect influence in the defeat of Balor thousands of years later, when his severed head was hurled into the Great Devoid, destroying The Leveler forever.

Trivia
In Irish mythology, a Callieach is a divine hag that can wield powerful elemental magics.