Zarathushtra (Modern Persian: زرتشت‎, Zartosht), was an ancient Iranian prophet (spiritual leader) who founded what is now known as Zoroastrianism. His teachings challenged the existing traditions of the Indo-Iranian religion and inaugurated a movement that eventually became the dominant religion in Ancient Persia. He was a native speaker of Old Avestan and lived in the eastern part of the Iranian Plateau, but his exact birthplace is uncertain