Origins
The Elder Gods are creatures that were shaped from Effluvium and matter by unknown entities, dozen of millennia ago. Their physiology was based on life forms present on the planet such as early Humans and Elkars. They were made of inert matter, with a nervous system and a brain infused with Effluvium to bring them to life.
Their purpose was to collect Effluvium and create a complex machinery to refine and condense it, and send it to their maker’s world through a portal.
Almost all Effluvium had been collected from the Mortal world, and some was left in the Otherworld. When several of them died, the Elder Gods understood that they were coming to the end of their lifespan. They plotted against their masters, and managed to secretly forge Cores supercharged with highly condensed Effluvium. Each God merged with a Core to empower themselves and prolong their life. With their newfound power they repelled their makers and closed the portal to their world.
Every year, an echo of the power overload that happened when they fused with their Cores affects the Gods and places them in a state of weakness for a day.
Diaspora
The Gods, solitary by nature, spread through the earth and established dominions on which they became the unquestioned rulers.
Some Gods appeared to less powerful creatures, such as Humans, Kurgaun and Elkars, and ruled them.
Other Gods decided to stay on their own, finding fulfillment in showing the world how powerful they were by haunting and slaughtering.
Reign
The pattern followed by most Gods was to establish a central palace, or temple, in the Otherworld, and create a portal to the Mortal World so that worshipers could cross on certain dates to worship them.
The Otherworld was more populated than the Mortal World so the Gods generally preferred to reign from there.
Many ruling Gods had conflicts with their neighbours, with populations spreading and conquering from one area to the other. Yet the Gods themselves were of equal power and unable to destroy one another, resulting in a status quo. Some Gods has to flee their dominions, establish anew elsewhere — some became roamers, others built new kingdoms.
Communication
Despite their internal conflicts, the Gods communicated at regular intervals. They did not meet in person, but communicated through their power, each year at the anniversary of their initial split.
Unexpected End
Unforeseen by the Gods was the fact that the Cores of their power had a limited lifespan, and was prone to imperfections, rendering them unstable after millennia of use.
Tuanat was the first God to realise this, and tried preventing more deaths — yet she was only met with disbelief and derision. The other gods were not so lucky, and their Cores exploded one after the other, killing them in the process.
Soon, the Gods were gone, as were the portals between the worlds — too weak to make the worshippers cross, without the power of the Gods to help it. From there on the two worlds were truly separated. Creatures on each world shaped new beliefs, new gods, after themselves.