The Zoroastrian religion, or Mazdayasna, is the pre-Islamic religion of Iran. It was founded sometime before the 6th century B.C.E. by the prophet Zarathustra (known to the Greeks as Zoroaster).
Zoroastrianism is a dualistic religion; that is, it ascribes to a worldview in which the universe is composed of polar opposites, such as Light and Darkness, Good and Evil, and Order and Chaos. Both the physical and spiritual realms exist in a state of constant tension between these opposing forces. Spiritually, these opposites are embodied in the benevolent supreme god, Ahura Mazda, who represents goodness, creation, and life, and his nemesis, the chaotic spirit Ahriman, who represents evil, destruction and death. It is the duty of every person during their lifetime to "fight" for Ahura Mazda to help the god overcome the forces of chaos represented by Ahriman.
Ahura Mazda is omnipotent and omniscient, but he does not rule the universe alone. To aid him, he created six beings known as the Amesha Spentas, or "Bounteous Immortals." These beings are similar in nature to the angels of the Abrahamic faiths, but they are also metaphors for spiritual goals each person should try to attain. The Amesha Spentas are:
Vohu Manah — Good mind and good purpose.
Asha Vahishta — Truth and righteousness.
Spenta Ameraiti — Holy devotion, serenity and loving kindness.
Khashathra Vairya — Power and just rule.
Hauravatat — Wholeness and health.
Ameretat — Long life and immortality.
People must work to achieve the Amesha Spentas every day. When a person dies, their soul will be judged according to their deeds in their lifetime. Those who performed more good acts than evil acts will enter Heaven, while those who performed more evil acts than good ones must go to Hell. Zoroastrianism also accounts for a concept of Purgatory, where the souls of those people whose good and evil acts precisely balance each other are sent.
Ahura Mazda and Ahriman are constantly at war, both in the larger world and in the soul of each person. Ultimately, this war will lead to a final confrontation—an apocalypse—in which Ahura Mazda permanently defeats Ahriman, after which all beings will live in bliss and harmony. Before this final war, there will be periods in which Ahriman seems to be prevailing, but Zarathustra predicted that "sons," or descendants, of his would appear in the world at these periods just in time to tip the balance back in favor of Ahura Mazda.
The belief in a final battle makes Zoroastrianism an eschatological religion, while Zarathustra's predictions about his descendants appearing to save the world make Zoroastrianism a messianic religion. These features, as well as Zoroastrianism's fundamental dualism, heavily influenced the development of both Christianity and Islam.
Zoroastrianism is a living tradition, although since the advent of Islam, it has dwindled to a very small community of fewer than 200,000 people worldwide. Most of the community is based outside of Iran, in India, Iraq, Kurdistan, and Central Asia.