Zoroastrianism might be called the obscure religion that shaped the West:
It is generally believed by scholars that the ancient Iranian prophet Zarathustra (known in Persian as Zartosht and Greek as Zoroaster) lived sometime between 1500 and 1000 BC. Prior to Zarathustra, the ancient Persians worshipped the deities of the old Irano-Aryan religion, a counterpart to the Indo-Aryan religion that would come to be known as Hinduism. Zarathustra, however, condemned this practice, and preached that God alone – Ahura Mazda, the Lord of Wisdom – should be worshipped. In doing so, he not only contributed to the great divide between the Iranian and Indian Aryans, but arguably introduced to mankind its first monotheistic faith.
The idea of a single god was not the only essentially Zoroastrian tenet to find its way into other major faiths, most notably the ‘big three’: Judaism, Christianity and Islam. The concepts of Heaven and Hell, Judgment Day and the final revelation of the world, and angels and demons all originated in the teachings of Zarathustra, as well as the later canon of Zoroastrian literature they inspired. Even the idea of Satan is a fundamentally Zoroastrian one; in fact, the entire faith of Zoroastrianism is predicated on the struggle between God and the forces of goodness and light (represented by the Holy Spirit, Spenta Manyu) and Ahriman, who presides over the forces of darkness and evil. While man has to choose to which side he belongs, the religion teaches that ultimately, God will prevail, and even those condemned to hellfire will enjoy the blessings of Paradise (an Old Persian word).
How did Zoroastrian ideas find their way into the Abrahamic faiths and elsewhere? According to scholars, many of these concepts were introduced to the Jews of Babylon upon being liberated by the Persian emperor Cyrus the Great. They trickled into mainstream Jewish thought, and figures like Beelzebub emerged. And after Persia’s conquests of Greek lands during the heyday of the Achaemenid Empire, Greek philosophy took a different course. The Greeks had previously believed humans had little agency, and that their fates were at the mercy of their many gods, whom often acted according to whim and fancy. After their acquaintance with Iranian religion and philosophy, however, they began to feel more as if they were the masters of their destinies, and that their decisions were in their own hands.