At the dawn of time, the cosmos was created. Scholars differ on exactly how the cosmos came into being, and gods have given different answers. Some believe the cosmos was created by the death of another cosmos. Some believe that once there was only the Astral Sea and the pure thoughts of gods. Some believe in the myth of the Light, the Dark, and the Serpent. For whatever reason, eventually the first god would emerge and create the world: The First Dragon.
The First Dragon created the Primordials of Earth, Water, Fire and Water and the first gods and set them free in the world. Using the elements of the Priomordials, the gods created as they saw fit, and they would couple to create new gods.
The Material Plane was created and the Outer Planes, all existing as one in this age. Light was ever present in the world through the presence of the Fire Primordial and creation was simple for the gods, lending power from the Primordials.
The gods would also create the first mortals, those now known to us as the Ancients.
In time, another type of being would creep into the Cosmos from beyond: the Demons and their Abyss. To combat them, the gods created the celestials, who kept the Cosmos and the mortals free of demonic influence.