From Avestan Demon to Persian Tyrant

By the time Ferdowsi composed the Shahnameh, the Persian national epic completed around 1010 CE, Azi Dahaka had been reworked into Zahhak, a human tyrant rather than a cosmic serpent outright, though the serpents remain: two snakes said to grow from his shoulders after a kiss from Ahriman's agent, each demanding to be fed a human brain daily to keep from devouring Zahhak himself. Zahhak seizes the throne from the legitimate king Jamshid, whose own story the Avesta and the Bundahishn preserve independently as Yima, and rules as a monster of misrule until the blacksmith Kaveh raises a rebellion and the hero Fereydun, a continuation of the Avestan Thraetaona under a later name, overthrows him and binds him at Mount Damavand.

The transformation illustrates how a single mythic structure, a chaos serpent whose defeat restores rightful order, persisted across more than a thousand years and a shift from religious scripture to secular epic, carrying its core opposition essentially unchanged while its surface details, name and genre all changed around it. Mary Boyce and later historians of Iranian religion treat the Avesta to Shahnameh transmission of Azi Dahaka or Zahhak as one of the clearest cases of Iranian religious myth surviving Islamic conversion by migrating into national literature rather than continued cultic practice.