Also known as Zarathustra, Zarathushtra Spitama, or Ashu Zarathushtra — was the prophet of ancient Iran, whose transformation of his inherited religion, Zoroastrianism, inaugurated a movement that eventually became the dominant religion in Iran up until the triumph of Islam. He was a native speaker of Old Avestan and lived in the eastern part of the Iranian Plateau, but his exact birthplace is uncertain.