- You may be looking for the planet of the same name.
The Keth was a perpetually shifting organism which took traits from the organisms it enveloped. When it was first awakened, it took the appearance of a yellow ooze, but as it grew it took on different forms, including a massive humanoid form. (PROSE: St Anthony's Fire)
The Keth was created to eliminate evolutionary dead-ends by consuming organisms which endangered the environment or were genetically stagnant. Unfortunately, its standards were set too high and it started to destroy all life on Betrushia. The Betrushians stopped it by placing satellites around Betrushia, trapping it in the centre of the planet. After millions of years, the planet recovered from the destruction. The second Betrushians, who evolved after the event, retained a race memory of the Keth as a force of evil destined to destroy the world.
In 2148, the Chapter of Saint Anthony came to Betrushia and their ships destroyed some of the satellites that kept the Keth at the planet's core. The Keth awoke, destabilising the planet. The Betrushians took the ships from the Chapter of St Anthony and used them to boost the power of the satellites until the planet destroyed itself and the Keth with it. (PROSE: St Anthony's Fire)