Zoroastrianism is a dualistic(二元論の)religion founded by Iranian prophet and religious poet Zoroaster, who lived between 628 and 551 BCE. At the age of 30, Zoroaster had his first vision and began teaching that Ahura Mazda was the highest god and alone was worthy of worship - a concept that rejected the polytheism practiced in Iran at the time. His attempts to proselytize(改宗させる)initially failed, but after he converted King Vishtaspa, the religion rapidly spread.