Implanted Chaos

The chaos and initial seeding of the chaos seeds were planted by a mad stone giant dream walker (Volos guide page 154) whose expose and lack of grasp on reality drove him into a state of delusion, and thus the idea of messing with the dream world seemed of little consequence. It started commanding it's ettin servant to give false prophecies and instructions to humanoids who would seek it's aid. He bargained with a witch coven, offering rare ingredients and objects it had collected on its travels around the world in return for giving the same prophecies. The last is a blue abashi page 163 mords tome, who was convinced to mislead the people of cedarwood in exchange for the giant to later pledge allegiance to Tiamat, and for his madness to be cured. This evil pact change the demon from being a slightly crazy giant into being a truly evil being, changing through the powers of the devilish magic pact into a stone giant quintessent with evil intentions, who later uses his newfound powers to use thunderstorms as license to commit terrible acts on innocents, and force others to bargain with devils to save themselves, increasing the hold of tiamat over the land. 
The whole event however, was iniitiated by a sorceror turned warlock who sought to throw any suspicious researchers off his tail by creating a great distraction of changing the end of the world prophecies regarding him into those related to the end of the empiric peace and the return of Yeenagu and his hordes.