The old gods

The old gods are immortal beings that were spontaneously created from the Stream. They are responsible for the creation of all planes and allowing mortals to use magic.

History
When the old gods came into existence, they began to create their own personal planes, which they controlled every aspect of. Eventually they grew bored with this and created a new plane, and populated it with people of free will. The proximity to the stream caused the people there to mutate into hideous beings. They abandoned that plane, creating a new set of planes, protected from the stream by wards. The new set of planes contained the material and elemental planes, along with the ability to create new planes. An unfortunate side effect of the ward was that they would not be able to influence the plane, so they created gods to watch over them and ensure that they prospered.

Magiri remained in the old material plane and directed the flow of the stream into the new planes so that they could use magic, but not enough that it would destroy them.

Cults
Cults to the old gods are extremely rare because the old gods cannot influence the planes in any way. The cults that do exist usually worship the god as the embodiment of the element rather than the god itself.