Introduction
Angra Mainyu, "Destructive Spirit" (later Ahriman in Middle Persian), is the personification of evil, falsehood and destruction in Zoroastrian cosmology, the opposing force to Ahura Mazda. Unlike a fallen angel or a god's rival in some other traditions, Angra Mainyu is understood in Zoroastrianism as an independent, uncreated principle of non-existence and chaos, whose eventual and total defeat is assured by prophecy.
This article follows the Zoroastrian and Shahnameh traditions, noting where the older Avestan material and Ferdowsi's later epic differ.
The twin spirits
The Younger Avesta describes Ahura Mazda and Angra Mainyu as twin spirits (though later Zoroastrian theology increasingly separates them, with Ahura Mazda alone regarded as the true creator) who, at the dawn of existence, made opposite choices: Ahura Mazda chose asha, truth and order, while Angra Mainyu chose druj, the Lie, deception and disorder.
Assault on creation
Zoroastrian mythology, especially the Pahlavi text Bundahishn, describes Angra Mainyu as attacking each part of Ahura Mazda's good creation in turn, introducing death, disease, noxious creatures, and moral corruption into a world that had been made originally perfect. He is the source of the daevas, the demonic beings who oppose the Amesha Spentas and Yazatas.
In the Shahnameh
In Ferdowsi's later epic the Shahnameh, Angra Mainyu (as Ahriman) appears in a more folkloric, less strictly theological role, working through demons (divs) to corrupt kings: he is said to have killed Keyumars's son Siyamak through his own son, the Black Div, kissed the shoulders of the tyrant Zahhak to grow serpents there, and generally acts as the hidden source of Iran's political and moral troubles across the epic's early legendary history.
Ultimate defeat
Zoroastrian doctrine holds that Angra Mainyu's power, though immense, is not eternal: at Frashokereti, the final renovation of the world, he will be permanently defeated and rendered powerless, and evil will be eliminated from existence entirely.