Zoroastrianism is considered the forerunner of monotheistic religion. The religion began in what is now Iran. The number of Zoroastrians currently living is small, in communities in India, persecuted communities in Iran, and a diaspora mainly in the English-speaking world. The "You will be assimilated, resistance is futile" aspect of Islam in Iran is responsible for the decimation of Zoroastrians. The religion is especially important as the wellspring of Abrahamic monotheism.
While I rely quite a bit on Wikipedia, the page on Zoroastrianism appears biased in favor of the religion, almost an ad for Zoroastrianism.
According to Robert Pollack's "The Everything World's Religions Book":
*There are about 150,000 current members.
*Origin is about 660BCE
*Founder was Zoroaster (his Greek name), also known as Zarathustra (Middle Persian name) or Zarthosht (In India or Persia)
*The legend of Zoroaster is thathis mother was a virgin, and he was conceived by a visiting shaft of light. Instead of crying at birth, he laughed. He helped his father tend cattle. Little else is known until he reached 30 years old. He was educated as a priest, and wandered the wilderness practicing meditation.
*God appeared to him. "God" was also known as Ahura Mazda, "The Wise", and taught Zarthosht about the true religion.
*Zarthosht then went around trying to convert people. He was tested by King Vishtaspa's magicians, who asked him 33 questions in 3 days; he passed and they unsuccessfully tried to frame him as a witch. His breakthrough occurred when he cured king Vishtaspa's horse of paralysis.
*Zarthosht died when stabbed by an infidel soldier. He was 77 years old at the time.
Zoroastrian belief systems include a creation myth, deities, rules for living, and afterlife.
... the world created by the deity Ahura Mazda. The great mountain, Alburz, grew for 800 years until it touched the sky. From that point, rain fell, forming the Vourukasha sea and two great rivers. The first animal, the white bull, lived on the bank of the river Veh Rod. However, the evil spirit, Angra Mainyu, killed it. Its seed (ie, semen) was carried to the moon and purified, creating many animals and plants. Across the river lived the first man, Gayomard, bright as the sun. Angra Mainyu also killed him)....The sun purified his seedfor forty years, which then sprouted a rhubarb plant . This plant grew into Mashya and Mashyanag, the first mortals.Instead of killing them, Angra Mainyu deceived them into worshipping him. After 50 years they bore twins, but they ate the twins, owing to their sin. After a very long time, two more twins were born, and from them came all humans (but specifically Persians).
Ahura Mazda is the supreme deity. The monotheistic concept replaced polytheism.
Ahura Mazda had 2 children, Spenta Mainyu (good) and Angra Mainyu (evil) (why isn't this polytheism?)
Angra Mainyu opposed Ahura Mazda, who had become the evil spirit of violence and death. (hence, dualism)
Rules for living, From Philip Wilkinson's "Religions":
Zoroastrianism requires that each person knows good from evil. Humans can make moral distinctions, which is what makes us different from other animals. Personal responsiblity and morality are vital. These include praying, ritual purification, propagation of the beleif by marrying a Zoroastrian and reproducing, honesty, charity, humanitarianism, eat moderately, keep promises. Be tolerant and forgiving toward others. Make your enemies into friends. Persuade sinners to reform, and teach the 'ignorant'. "Good thoughts, good words, good deeds". Zoroastrianism condemns anger, greed, idleness, arrogance, adultery, vengefulness, bad language, violence, and apostacy.
The dead are exposed on high platforms, for consumption by vultures. This method avoids polluting the earth through burial, and avoids polluting the sky through cremation.
Disclosure: I'm no religious scholar. Please feel free to correct any errors I have made. This discussion is intended to enlighten, regarding understanding of, and history of, religious belief - not to promote, support, or condemn.