Azhi Dahaka

In the Avesta

The Zamyad Yasht calls Azhi Dahaka 'the three-mouthed, the three-headed, the six-eyed, who had a thousand senses, that most powerful, fiendish Druj', created by Angra Mainyu against the material world. He struggles with Atar, the fire, for possession of the royal Glory, and is smitten by Thraetaona, heir of the Athwya clan. The Vendidad names the land of Varena as the place 'for which was born Thraetaona, who smote Azi Dahaka', and the Greater Bundahishn, as Darmesteter noted, identifies that land with Mount Damavand, where the dragon was bound with iron bonds. The Aban Yasht says that he sacrificed to Anahita, asking to empty the seven regions of the earth of men, and that she refused him.

Zahhak

In Ferdowsi's Shahnameh the dragon has become a human king, Zahhak, whose shoulders sprout two serpents after the Devil kisses them and who feeds the serpents on human brains through a reign of a thousand years, until Fereydun, the epic form of Thraetaona, overthrows him and chains him in a cave in Mount Damavand.

At the end of time

Middle Persian tradition holds that near the end of the world Dahag will break his bonds and ravage creation until the hero Keresaspa is raised to kill him, one of the events that lead to the final renovation.