 Khyber, the Dragon Below, is the name given to the underworld, and is similar to the Underdark in many other settings.According to the creation story, the world was formed when the progenitor wyrms changed their form into what they are now.Siberys created the dragons, Eberron created humanoids and other "lower races", and Khyber created the "demons" of the world (The term "demons" is meant to use the common definition, not the D&D outsider).