The Jormundsaga

Oh Jormungandr, mightiest of the starry seas! Sangving slew you, jealous of your throne Now your flesh is naught but a feast for trees, The mountain peaks formed of your bone!
- Stanza 142, the Jormundsaga
The Jormundsaga is the name of the oldest legend known to Tyrian mythology. Although Tyrians do not worship the Oroboros, the world-snake does appear in the account of the creation of the world in that faith.
In the Jormundsaga, the universe began with the awakening of a primordial serpent, called Jormundgandr (World-Snake). Jormundgandr's skin was the starry sky; the earth its flesh; the mountains its bones. Folk - as sentient beings are collectively referred to in the Jormundsaga - were caretakers, groomers, and gardeners of Jormundgandr's flesh, pruning it and enhancing its beauty in exchange for food and shelter. The Folk quickly created a beautiful garden out of Jormundgandr's living flesh. 
Yet one group of Folk, who tended to be more curious about the world - the Alvr - were unsatisfied with merely serving Jormundgandr. Wanting to tame the serpent, they created an avatar out of their own blood, called Sangving. Sangving, or Sanguine, as she is now known, slew the World-Snake, chopping it up into many pieces, fracturing the worlds of the universe into many smaller ones, and splitting the Folk into many different races. The Alvr survived, some of them staying loyal to Sanguine, others rencouncing and fighting her. The humans, meanwhile, remained, harried by cold, vampires, and other monsters, until Tyr was summoned. But that is another saga entirely.