Ouroboros

Ouroboros, also spelled Ourubourous, is a mythical giant serpent from Vahnatai mythology. It encircled the whole world and ate its own tail, devouring itself. In Vahnatai lore, this tale is meant to symbolize the corruption of absolute power, and the constant risk of being destroyed by one's own pride and arrogance. Notably, among some humans, the image (not the story) of Ouroboros biting its own tail has become a symbol of eternity and balance, signifying the circle of life.

The crystal soul Glantris-Bok in Ghikra related the tale to the surface explorers thusly:

Ouroboros was the snake of legend, that was so mighty it encircled the world and ate its own tail. It was all-powerful, and yet devoured itself.