It is believed by some during the 7th century B.C.E., while the powers west of the Zagrus were in bitter battle, a man by the name Zarathustra (in Greek: Zoroaster) appeared on the eastern scene. His origins are unknown - some sources claim him to be Medean, while others suggest that he was Bactrian or perhaps Persian, and the date of his ascension unto existence is also debated; more recent estimates have placed him somewhere betwixt the 16th and 11th centuries B.C.E. He reformed the polytheistic religion of the Iranians, which was rooted in Aryan lore, creating a distinct dualism of good and evil later to be inheritted by the Christians through Mithraism. The god Mithra, at this time, was one among many gods worshipped, although so as not to make the fatal mistake of minimalizing his position, he clearly claimed a prominent position within the pre-zoroastrian pantheon of Iran - this can be evinced in the fact that as through Zoroaster's reformations, where many of the the ancient gods were classified as evil forces, and only a few remained on the side of Zoroaster's 'one god' Ahura-Mazda, Mithra claimed the position of the most prominent yazata (yazata being an old Iranian designation for 'god' - they were the divine elements to whom the hymns were addressed to in the Zend-Avesta).

The Iranians had two broad classifications for supernatural beings: the daeva, which were the good spirits of light (and whence comes the term devil) and Ahura which corresponded with the more sublime and awful spirits. Zoroaster elevated one such Ahura unto the highest levels, reversing his role into the single powerful god of the universe; in turn, the daeva were lowered to an evil status (whence the term devil gathers it's evil connotations) as is noted in the Avesta. Onto the name Ahura, Zoroaster spliced the epithet mazdao, meaing "the wise." This Wise Lord, or Ahura-Mazda (later called Ormazd), was the All-Father and was the primaeval spirit whence this world sprang. The course of this world was governed by his foreseeing eye; his good will is brought forth by his guiding spirit Spenta Mainyush (trans. Holy Spirit) and was opposed by his brother, Angro-Mainyush (later called Ahriman).

Zoroaster's reformations particularly focussed on strong morality. He also borrowed from the ancient Aryan conceptions of truth, as are also present in the Vedic traditions of India, and even incorporated an ancient Aryan fire ritual, stripping Indra as the designated god for whom it was done and replacing Ahura-Mazda in his place. The religion of Zoroaster was fundamentally characterized as a battle between good and evil - between those forces under the command of Ahura-Mazda and those under the command of Angro-Mainyush. A final apocalypse is spoken of in which the forces of good will triumph, after which, a final judgment will occur; and mentioning of a new prophet, the Saoshyant, is made that will come and finally rid the world of all evil.

As for the nature of the beliefs of the afterwordly, an eternal heaven and hell were posited. The works of every man were noted in the Book of Life and, eventhough, a wicked actions could not be undone, a surplus of good actions could counter-balance them. The object of the war between good and evil was man's soul, and man, through every action was a participant in this battle. Good was upheld by upholding truth (not bearing false witness), doing good deeds, keeping good thoughts, speaking good words and keeping both his soul and body pure, while. every evil deed, thought, word, and lie increased Angra-Mainyush's power. Upon death, the soul arrives at the cinvato peretu, or accountant's bridge, across which lies the way to heaven. Here the life deeds are read out and a judgment is passed. If it so happens that the good and evil deeds equal each other, then there is a third realm that the soul is sent to, termed Hamestakans, and one's fate is not decided until the last judgement, called aka. Final judgment would, however, not occur until the apocolypse, when a final decisive battle would rage; upon Ahura's victory a final kingdom with earth and heaven united would flourish. Zoroaster understood that the revelation given him by the Good Spirit as a last resort by Ahura to attempt at saving the inhabitants of the world. The apocalypse was understood as soon to arrive - even in his lifetime did he expect for the end to come.

This was, essentially, the form in which Zoroaster's religion first appeared - bereft of any particular rites, save the fire ritual, and focussed on an abstraction of good and evil. This was, as one would expect, too alien to people used to worshipping more corporeal deities. As such, eventually, the more ancient Aryan deities were revived - among them Mithra. Other modifications included a ritualization of the religion - absolution for the cleansing of sins was accepted, and the time for the apocalypse was extended to occur at the end of a long 3000 year cycle.