The Great Wyrms

Know you the power of Great Kor and all his creations, then you know the power of the Wyrms. They were created first by the ancient god, and with their aid he crafted all of Cadash. In time they spread across the new land guiding its shape and shepherding the animals. But Chaos was already at hand, and soon some of these great creatures became twisted and hateful. They turned against each other, and the world of Cadash was rent asunder. It was in this time that Kor arrived on Cadash to tame his own creations.

- A telling of the The Great Wyrms

Summary

The story tells of Kor's creation of life upon Cadash, including the first dragons that aided him in his work. The first of these was the great Osu, but other dragons (or Wyrms) followed. These creatures were strongly tied to their environment and the elements around them.
Soon enough Chaos was unleashed upon the Wyrms and some were corrupted and twisted. Their natural pride and desire was twisted into a dangerous combination of arrogance and greed. Soon the dragons were fighting each other and destroying many of the plants and animals that Kor created.
Kor himself arrived upon Cadash and met with Osu. Together the two wove powerful magic that would untwist the minds of the dragons that weren't too far gone. But soon the other banded together and battled the God and his creations. This was the first great war ever on Cadash, and Kor wept that it occurred.
In the end the corrupted dragons were defeated. Some were destroyed completely, but others were buried in mountains (becoming volcanos) and others were submerged in the seas (causing whirlpools) and others were locked in the very ice they created. The battle was costly, and so few Wyrms were left. Osu and his remaining people went into hiding at the urging of Kor. Their powers were to work subtly but from afar.
As Osu vanished into the dusk it is said that Yeno's first children appeared in the moonlight, and the second age of Cadash began.

Historical Basis

Such a tale is beyond ancient, and occurred when the only writing known was the sigil and symbols of magic that Yeno, Kor and Osu created in those far off times. There are ancient writings by elven standards that record some of these events, but even those texts written millennia ago were long distant from the events recorded.
These days the story of Kor and the Dragons is merely told as part of the First Age of Cadash. Only the oldest and most obsessed elven scholars know more about this story. But it is said that first folk tell the tale of the Wyrms and Osu in particular. They see them as a guiding force that may help them in dark times.

Spread

Dragons are always popular in fiction, and appear constantly in stories. While this origin story of dragons is well known enough, it is usually nothing more than a few sentences about Kor creating dragons and Osu being their leader. Corruption is rarely mentioned and if it is, it is only said that Kor's the dragons were the first and most vulnerable to Chaos, something that many First Folk love to point out.

Variations & Mutation

Each race in Cadash seems to have a variation of this tale. Elven scholars have the most detailed, but The Story of Emid contains a version in which Emid tells the old story to a cleric of Ashtyr noting that even Kor's good intentions were not enough to stop the powers of Chaos, even in his most prized creations.

Cultural Reception

Most folk enjoy the story, and some religions even use it to show that Kor, one of the great Gods, was fallible in his decisions. Sometimes this is used to show humility. Other times it is used to show that Kor is an unworthy god. 
Osu's role in the story changes depending on the teller. Sometimes it is Osu alone who defeats the evil dragons and saves Cadash. Other times, Kor is riding around on the great Dragon blasting evil Wyrms with arcane power, and the dragon lord is not much more than a steed.

In Art

A famous painting by a halfling painter Roulf of Bailywick depicts a massive dragon rising over a weeping green figure. The agony and sadness is clearly captured in the grieving Kor as the monstrous black and silver dragon looms in front of him, looking both magnificent and revolting at once. It is considered Roulf's masterpiece and is hanging in the Shire Reeve's home in Oldholm.