Angra Mainyu or Ahriman is the "evil spirit" in the dualistic religion of Zoroastrianism. Angra Mainyu is the adversary of Ahura Mazda, the god of good.
The name does not occur in the Old Persian inscriptions. In the Avesta he is called the twin-brother of the Holy Spirits, and contrasted either with the Holy Spirit of Ahura Mazda or with Ahura Mazda himself. He is the all-destroying Satan, the source of all evil in the world and, like Ahura Mazda, exists since the beginning of the world. Ahriman chose evil consciously, and by this act he created death. Eventually, in the great world catastrophe, he will be defeated by Ahura Mazda and disappear. The later sect of the Zervanites held that both were visible manifestations of the primeval principle zruvan akarana (infinite time).
The central subject of Zoroastrian teaching and theology is the constant ongoing battle between Angra Mainyu and Ahura Mazda.