The Gods walk among us, and we are created in their image. Literally. We are elves, orcs, dwarfes, pechs, goblins... And so are they.
Nobody knows where they come from, but a few generations ago the humans arrived to our world. They have no God, no creater. They come from Nothing. Even the Gods are unable to know what happened, who made them.
At first they were a curiosity... Now, they might be the spark that starts a new God War.
Every 10 years the City of Gods reappear in the Deepsea, and the mortals can access their city, visit their temples and if they are lucky, meet their own Gods. The City of Gods is vast, marvelous and dangerous.
In the years in between, the Avatars are the major representants of the Will of the Gods. They are the paladins of their pantheons, and their actions mirror the divine will. There's one Avatar for each of the pantheons, and when they die or retire, the Gods are the ones in charge of selecting a new one.