In an earlier version of this religion, they both are the sons of Ahura Mazda (Ormazd). But later there is no longer a distinction between him and Ormazd, and they become one and the same god. His name, Spenta Mainyu, is after that no longer used. He still is the twin brother of Ahriman, but now their father is the primordial god Zurvan.
In ancient Persian mythology, Spenta Mainyu ("holy spirit") is the god of life and the personification of the good and the light. He is the twin brother of Angra Mainyu (Ahriman), the god of darkness, with whom he fights an eternal battle.