Zahhak is an evil figure in Iranian mythology, evident in ancient Iranian folklore as Aži Dahāka, the name by which he also appears in the texts of the Avesta. In Middle Persian he is called Dahāg or Bēvar-Asp, the latter meaning “[he who has] 10,000 horses”. Within Zoroastrianism, Zahhak (going under the name Aži Dahāka) is considered the son of Angra Mainyu, the foe of Ahura Mazda.
Aži (nominative ažiš) is the Avestan word for “serpent” or “dragon.” It is cognate to the Vedic Sanskrit word ahi, “snake,” and without a sinister implication. Azi and Ahi are distantly related to Greek ophis, Latin anguis, Russian and Old Church Slavonic уж (grass-snake), all meaning “snake”.
Despite the negative aspect of Aži Dahāka in mythology, dragons have been used on some banners of war throughout the history of Iranian peoples.
The Azhdarchid group of pterosaurs are named from an Persian word for “dragon” that ultimately comes from Aži Dahāka.
Aži Dahāka is the most significant and long-lasting of the ažis of the Avesta, the earliest religious texts of Zoroastrianism. He is described as a monster with three mouths, six eyes, and three heads (presumably meaning three heads with one mouth and two eyes each), cunning, strong and demonic. But in other respects Aži Dahāka has human qualities, and is never a mere animal.
Aži Dahāka appears in several of the Avestan myths and is mentioned parenthetically in many more places in Zoroastrian literature.
In a post-Avestan Zoroastrian text, the Dēnkard, Aži Dahāka is possessed of all possible sins and evil counsels, the opposite of the good king Jam. The name Dahāg (Dahāka) is punningly interpreted as meaning “having ten (dah) sins.” His mother is Wadag (or Ōdag), herself described as a great sinner, who committed incest with her son.
In the Avesta, Aži Dahāka is said to have lived in the inaccessible fortress of Kuuirinta in the land of Baβri, where he worshipped the yazatas Arədvī Sūrā (Anāhitā), divinity of the rivers, and Vayu, divinity of the storm-wind. Based on the similarity between Baβri and Old Persian Bābiru (Babylon), later Zoroastrians localized Aži Dahāka in Mesopotamia, though the identification is open to doubt. Aži Dahāka asked these two yazatas for power to depopulate the world. Being representatives of the Good, they refused.
In one Avestan text, Aži Dahāka has a brother named Spitiyura. Together they attack the hero Yima (Jamshid) and cut him in half with a saw, but are then beaten back by the yazata Ātar, the divine spirit of Fire.