Was the Shah of Iran a Muslim?

The Shah of Iran is a title for the Kings of Persia stretching back to antiquity, even preceding Islam. Some of the Shahs, such as those of the Parthian and Sassanid Dynasties were Zoroastrian. All Shahs of Iran after the year 800 C.E. were Muslim and All Shahs of Iran after 1550 C.E. were Shiite Muslims.