A Who's Who of World Mythology : Azhi Dahaka

Azhi Dahaka was a Druj, an enemy of the asha or universal law. The name seems also to have been borne by a dynasty of serpent worshiping kings in Media. According to the Zoroastrian creation legend, Azhi Dahaka is the three-headed serpent demon-dragon that overthrew Yima, the first mortal by cutting him in two. One head was the embodiment of pain, one of anguish, and the last of death. Its wings were so large and dark they blotted out the stars.

Eventually, Atar, “fire,” caught Azhi Dahaka after a fight over land, air, and sea and chained it to a mountain. Ultimately, Azhi Dahaka became the symbol of falsehood and the servant of Ahriman. It was believed that Azhi Dahaka would break free of its chains at the end of time and ravage the lands once more. The hero Keresaspa would then hunt down and kill the monster.