According to Zoroaster, Ahura Mazdā created the universe and the cosmic order that he maintains. He created the twin spirits Spenta Mainyu and Angra Mainyu ( Ahriman)—the former beneficent, choosing truth, light, and life, the latter destructive, choosing deceit, darkness, and death. The struggle of the spirits against each other makes up the history of the world.

In Zoroastrianism as reflected in the Avesta, Ahura Mazdā is identified with the beneficent spirit and directly opposed to the destructive one. He is all-wise, bounteous, undeceiving, and the creator of everything good. The beneficent and evil spirits are conceived as mutually limiting, coeternal beings, the one above and the other beneath, with the world in between as their battleground. In late sources (3rd century AD onward), Zurvān (“Time”) is made the father of the twins Ormazd and Ahriman (Angra Mainyu) who, in orthodox Mazdaism, reign alternately over the world until Ormazd's ultimate victory.

Something of this conception is reflected in Manichaeism, in which God is sometimes called Zurvān, while Ormazd is his first emanation, Primal Man, who is vanquished by the destructive spirit of darkness but rescued by God's second emanation, the Living Spirit.