Creation myth: Skormir's dream
Skormir was the first being, who lived in the astral plane, dreaming of the future. When he awoke, he strove to make the world, and so made four creatures embodying the ideas in his dreams. These four children of Skormir made the other planes as they are, destroying Skormir in the process, and so creating death, and making people mortal. The builders commit themselves to giving old souls to new mortals.
The ideas about the planes, gathered over many years, are roughly continuous with the myth. Visitors to the ethereal plane often claim to hear four distant voices whispering an apology, although the name reported varies.
Variations of this story are told often around campfires in Tariksan, Samurella, Davmire, and to some extent Katarinash, Nadrow, and Kadrik. It is not told by the Yan'katar, but the slave population knows it well.
Variations & Mutation
The most common variation concerns what happened to Skormir. Sometimes it's death is the result of a plot between some or all of his children, sometimes it is so struck by the perfection of the four worlds it tears itself up so they can all exist. Sometimes Skormir is unhappy that the builders put their own ideas into the heads of the people, and refuses to bless any of the worlds, and the children either kill it or it tears itself apart so none of the worlds can be perfect.
Occasionally, Vathelod is credited with all of the creation of the arcana, and teaches only her people before becoming the routes for them between planes, with the other builders following suit afterwards.
While the story usually doesn't hold much divine importance, the various variations mean it suits many people's personal views about creation and the balance of life, so it is usually popular. Most bards and other storytellers know it (it's popularity in these circles assisted by the fact that Vathelod is the singer) and it's a peacefully familiar tale to the natives of Tariksan.
Many artists attempt to portray the four creating the planes, however as they have no agreed on form this varies wildly.