The Shattered World
Before the Primordials were locked away at the conclusion of the Dawn War by the gods, before either existed, before there was even a multiverse, there were the overgods, Ao and Ur.
Like the concept of Yin and Yang, Ao and Ur are complete opposites: Ao is creation; Ur is destruction. Ao’s ultimate triumph was the creation and population of the multiverse; Ur’s will be the complete destruction of it, like all those that have come before.
These are simple, inaccurate concepts, though, merely the attempts of limited mortal understanding trying to describe beings that defy description. Ao and Ur, despite being personified, are not individual entities, nor even entities per se — they are pure elemental forces, the purest that exist, even if they do not exist anywhere within the multiverse.
Occasionally, one or the other — usually Ur followed by Ao — will create or recruit an avatar to further their goals from within the multiverse. Most recently, Ur’s avatar was Kros; many believe that the souled vampire Taihou, who lead the opposition against Kros, was Ao’s avatar, although others believe Ao didn’t get involved this time.
Whatever the truth, Ur’s avatar failed, but not before doing severe damage to the multiverse, including outright destroying several minor demi-planes.