Most people know of the name Zarathustra only from Nietzsche's work, Thus spake Zarathustra, penned in the nineteenth century. Nietzsche believed that Judaeo-Christian morality and indeed religious morality in general was for slaves, unlike the morality that he extolled, the lifestyle of the hero, the great man whose greatness enabled him to transcend good and evil. [Note, ladies great man. Women, he thought, did not qualify.] Yet even more than Moses, Nietzsche blamed Zarathustra for the key tenet of religious morality, the idea that life was a battle between good and evil;and in this respect Nietzsche was probably right.
So who was Zarathustra? Estimates of his dates vary, ranging from 2000 to 600 BCE, but recent research has placed him about 1200, an intermediate date that is probably right. He was a priest of the ancient Iranian religion, and a peace-loving man who detested the wandering Aryan tribes who blighted the lives of the peaceable agriculturalists with whom he identified. These people worshipped the devas, especially Indra, while despising as lower deities the Ahuras [asuras] of the peoples that they dominated. Zarathustra staked his flag for the ahuras, despising the devas, and it is likely that from him we get the word devil.It is notable that Hindus still worship devas and relegate asuras to the nether realms
Zarathustra's religious experience came in a moment when he was gazing into a fire. He believed that addressing him through the flames was Ahura Mazda, the deity of light, truth and goodness. Mazda wanted to commission Zarathustra and his followers to work for his cause, promoting light, truth and goodness against the power of his arch-foe, Angrya Manyu, sometimes known as Ahriman. Ahriman was the force of evil in the world fighting against Mazda, and his technique was to use Druj, the lie. The religious experience in the fire has uncanny similarities to Moses' experience of the burning bush, which may have occurred two or three hundred years earlier. But since then the Zoroastrians have revered fire as sacred and so never cremate their dead, as death pollutes the sacred element. There is a Zoroastrian temple in Eastern Iran where a sacred flame has been burning since time immemorial as part of Zoroastrian worship.
Later Zoroastrian thought was to associate Mazda with seven assistants, the Amesa Spentas, the Bounteous Immortals, beings of archangelic status, one of whom was Mithras, whose cult was popular among Roman soldiers, and another of whom is still honoured now by the persecuted Yazidis of Iraq, who know him as the Peacock Angel.
It was the followers of Zarathustra who first realized that there would be a final battle between good and evil when the forces of goodness would be led by a saoshyant [saviour] when Ahriman would be defeated. They also believed that there would be a resurrection of the righteous dead to a paradisal condition.
You will notice that these ideas seem familiar, and they are. But the dispute is whether Zoroastrianism influenced Judaism or vice versa.There is no doubt that the two religions were in contact for many hundreds of years, so some interchange of ideas is likely.