 Regardless of the debate as to where Zoroaster was from, Zoroastrianism spread to become one of the world's most influential religions and became the main faith of the old Aryan people for centuries.It also remained the official religion of Persia until the defeat of the Sassanian ruler Yazdegerd III—over a thousand years after its founding—by Muslim Arabs.In what is today southern Iran, the Persians emerged to challenge Median supremacy on the Iranian plateau.