The gods forged world after world, creating peoples and culture and conflict and adventure. They created vast and intricate universes independent of one another in the vast infinity that is existence. And so these universes float on in the multiverse, completely unaware of the existence of the others, going on as the pantheon that created it desired. Then something occurred which was not intended: several of the universes collided, unbeknownst to their inhabitants. The resulting multiplane became, essentially, an entirely new universe, and was filled with all the souls that weren't fit for the universes that collided.
The gods of each universe gathered together and assessed the Multiplane, and what they saw was a land of conflict and evil; wretched abominations called monsters fought the "civilized" peoples, who were themselves chaotic, unkind, and mistrustful. Good was a rare thing in this new world...
The universes kept drifting. Every day this Multiplane comes closer to absolute destruction, closer to popping straight out of existence. The gods decided that, they will re-assess the universe before this destruction; if it is no closer to good, order, justice, and honor, then it will be let go into the void, abandoned to utter destruction. However, if there is progress, if there is a sign of light in this world of darkness, they will grant the world its own domain in the multiverse.
A couple of the more benevolent gods didn't want to see all the souls go to waste, didn't want to throw away this potential; They went to other universes, acquired the essence of heroes whose fate had been unkind, who were denied from other universes, and gave them a home and a purpose; they created a citadel in the land of chaos to house all the good people they had saved from oblivion, and hoped that they would make the world a better place, a good place.