Introduced 551 BCE.
On Origins: "The religion of Iran before the time of Zoroaster is not directly accessible, for there are no reliable sources more ancient than the prophet himself. It has to be studied indirectly on the basis of later documents and by a comparative approach. The language of Iran is closely akin to that of northern India, and hence the people of the two lands probably had common ancestors—the Indo-Iranians, or Aryans. The religion of the latter has been reconstructed by means of common elements contained in the sacred books of Iran and India: mainly the Avesta and the Vedas. Both collections exhibit the same kind of polytheism" (Britannica)