Creation Mythos
At the dawn of time, the world was populated by primordial entities expelled from the soup of a limitless cosmos. Things that gravitated to the planet as it coalesced out of the dark materials of the universe. For unlike the many cold, life-hating worlds surrounding it, Tamavara had the spark. The spark changed all that engaged with it. The spark was life. The spark sustained.
The primordial beings of the outer darkness (the Void), and the inner light (the Heavens), came together and formed the ecological matrix of the nascent world. From the murky depths of the World Sea, the first adapted organisms rose. Over thousands upon thousands of years, they developed, creating a vast variety of flora and fauna, all optimized to their environment. But though complex life was bountiful, precious little of it was capable of developing an intelligent or meaningful society of any sort. In fact, there were but two species with an intellectual level of perspective minimally required for the task. So it fell to the humans and the thri-kreen (mantis folk) to jump start civilization.
So it was that countless years ago, before the advent of recorded time, that our world witnessed the indelicate, initial attempts at organized society, fostered through both its human and thri-kreen populace. It is unknown which of these species developed first. However, what is known is that although the thri-kreen are physically superior to humans in many ways, they are not nearly as prolific. Humans, it seemed, had the numbers.
Along with the expansion of their distinct, burgeoning racial settlements, predictably came conflict and strife. There are currently only anecdotal fossil evidence as to the extent and frequency of these ancient, inter-species battles, but it is clear that the tribes of men and mantis folk were quite capable of decimating their opposing populations. And perhaps they would have both gone extinct if it weren't for the coming of the gods.
To the best of the records, the coming of the gods coincided with the advent of Mount Celene, the "holy mountain," and her decent from the very heavens above. The continents are not as they are today, and Celene's impact in the north of Hariel Majour triggered the seismic event that formed the mountain range known as The Unending Light that surrounds the Lake of the Sun.
It didn't take long for both man and kreen to discover the fallen mountain, and they both attempted to claim it for themselves. It is here that many faiths tell a different tale, as each seems to have their own human champion (the kreen do not seem to deviate down this path for their creation myth) who "took" Celene from the kreen and gained the praise of the gods within.
For though until this point, it lay quite dormant, the mountain was not without its own life. Within its hollow depths resided beings of such great power, they could only be referred to as gods (both greater and lesser). These god-beings made their intentions known. They required fealty from their "subjects" on Tamavara. They spoke to both man and kreen, in their dreams. They demanded submission from the mortals, based on nothing but blind faith. And this they received, thus creating the first of the world's religions.
It was once that the gods had the trust of the native tamavens that they opened their mountain home for the first time. For beyond dominating the hearts and minds of both man and kreen, the gods of Celene also created intelligent life of their own. The vanguard of their creations (sometimes collectively referred to as "godkin"), the titan-like giants and dragons, were the first to emerge from Celene, scouring the lands in search for something. Something clandestine to the native tamavens, primitive as they were.
For generations, men and kreen alike worshipped (and often battled) both giants and dragons, as the godkin expanded their territories across the globe. Those who worshipped them came to mimmic their societal structures, thus forming the first "modern" civilizations in the pre-historic era that pre-dated the Age of Light (A.L.). But the giants and their draconian allies soon became greedy. They began to fight amongst themselves, using the "small folk" of Tamavara as pawns in their battles for territory. The titans were no longer satisfied with their status as (what we assume to be) scouts and mappers of the new world. Instead, they desired dominion.
So it was that the greater forces of Celene, the very gods themselves, took matters into their own hands. They sent a new wave of minions to deal with the titan threat. Dwarves, goblinoids, and all races were created by the gods (aside from the Evaru), along with a multitude of vicious alien beasts of burden, were dispatched with orders to either retrieve or destroy both giants and dragons en masse. Either way, they could not be allowed to continue in their expansionist greed. Thus began the War of Titans.
Without expending too much time dwelling on the folly of this world wide battle, it's suffice to say that both sides lost many from their ranks, but it's the dragons and giants who were nearly wiped from the surface of the planet. As a direct result, the remaining of both species fled into hiding, doing their best to avoid direct conflict with either each other or the new inhabitants of Tamavera. By the time of the conflict's end, the proverbial genie had been already let out of the bottle, and the demi-human races of the gods' creation were loose upon Tamavara, intermingling with both humans and thri-kreen alike.
It's uncertain whether or not the gods wished to introduce their other children to the world at this point, or if their hands were forced due to the machinations of the titans. Regardless, the children of the gods, their perfectly designed servants and prodigies, were here, and like any other race, they began to proliferate.
Dwarves, goblinoids... they all served a particular purpose in service to their creators; a service which we, as mortals, are not privy to. Perhaps their original purpose came to an end the moment Celene alighted upon the world. Perhaps it was their duty to simply exist amongst the native beings of Tamavara. Or perhaps they were simply another part of what seemed to be a grand experiment. For the children of the gods were more than just similar in stature to the men of the world, they were also physically compatible.
Many of the extended races of our world are the results of these possible unions. Halflings, orcs, and half-orcs all originated in this manner, having mated between themselves or with humans.
Summary
Previous to the coming of the gods, the world was in chaos, under the loose rule of both humans and thri-kreen. Then came the descent of Mount Celene, and the release of its agents, the Godkin. The great giants and dragons brought order to the world but, over the vast years of their rule, they became increasingly greedy. The gods then released their "lesser" servants, in the form of an army of dwarves, and goblinoids. After a millennia of war, their combined forces purged Tamavara of the Godkin, with the few survivors fleeing - so they could perhaps still eke out a meager existence to this very day.
Once the servants of the gods were set upon Tamavara, they could no longer be returned to Celene. The gods granted them the ability to prosper amongst the humans and kreen, and thus they created homes and nation. They even bred with humans, who were compatible as a species. Many of the remaining intelligent "demi-humans" were birthed in this fashion. Halflings, half-orcs, isagorn... all of them the result of the union between themselves or each other.
Historical Basis
The faith of The Solaris originated the creation myth, which was later recorded by The Custodians of the Sun within The Solaris Tower. Prior to the formation of the city-state, records of this tale were kept and updated by the Grand Minister to the crown of Gorthain, representing the faith The Solaris.
Spread
Historically, the church tends to drive progress, especially with the written word, in service to the spreading of the gospel. During the Age of Destiny, members of the nascent Solaris found themselves under the spotlight, wielding a great degree of power. Countless scribes were conscripted to print the legend of our world's creation, often referred to as "The Book of the Harmonium" or just "The Harmonium," in order to attract more followers beyond those who could be swayed by the limited reach of their personal sermons.
It is the not-so-secret hope amongst those of faith that the continuing spread of the scriptures will prompt and influence the foretold "return of the gods" to the affairs of man.
Variations & Mutation
There are versions of the creation myth that include "characters," named participants in the crafting of our shared history. Typically, the humans have a champion, sometimes named Telga or Erantos, who stands up to the thri-kreen menace (in human-centric tales) in the race to claim Mount Celene. In these versions, the gods predominantly look like humans, and they reward Erantos for his prowess and leadership abilities. It's tales like these that are told in temples dedicated to the Solaris, and they comprise the basis behind the various pilgrimages to Celene that followed during the Age of Destiny.