caliph (n.)

late 14c., "ruler of a Muslim country," from Old French caliphe (12c., also algalife), from Medieval Latin califa, from Arabic khalifa "successor" (from khalafa "succeed"). The title given to the successor of Muhammad as leader of the community and defender of the faith; the first was Abu-Bakr, who succeeded Muhammad in the role of leader of the faithful after the prophet's death.