He is seen as the personification of evil, he leading the dark forces against the hosts of Spenta Mainyu, the holy spirit, who assisted Ahura Mazda, the wise lord, and final victor of the cosmic conflict. Ahriman introduced the frost in winter, heat in summer, all manner of diseases and other ills, to thwart Ahura Mazda, and he also created the dragon Azi Dahaka, who brought ruin to the Earth.
When Ahura Mazda created the heavens, Azi Dahaka sprung into the sky like a snake, and in opposition to the stars formed the planets. Both Ahriman and Ormazd were offspring of Zurvan Akarana, who had vowed that the firstborn should reign as king. Ahriman thus ripped open his mother's womb, and Zurvan pronounced that he should rule only for nine thousand years, after which period his twin brother should reign in his place.
Ahriman's chief weapon was concupiscence, through which all that was his should be devoured, even his own creation. There was a female counterpart of Ahriman, called Az, and it is said that when Ahriman saw the righteous man he swooned, and lay in a faint for three thousand years, until the 'accursed whore', Jeh, awoke him and defiled men with her destructive spirit, introducing fear, jealousy, lust and greed into man.
Ahriman lives in darkness, in a place where all those who do evil go to after their demise (Hell) and his symbol is the snake. He is what in Christian religion can be called Satan.