The Persian people had three major religions, which were Manichaeism, Zoroastrianism and the Baha'i faith. The Zorastrianism faith was the most well known and was based on the prophet known as Zoroaster.
Zoroaster wrote his ideas down in the "Gathas," which was a series of poems. The Zoroastrianism Holy Book became the "Avesta" and contained a large collection of his writings. The Manichaeism religion was based on the prophet Mani. After Mani's death, the religion barely survived. The Baha'i faith was an extension of Shi'a Islam at first, but became its own entity as time passed. It stressed the "oneness" of all people and things. Alexander the Great began to conquer the Persian Empire in 331 B.C. and the religions did not spread widely after the conquest.