After 1517, Ottoman sultans were commonly regarded as caliphs, the senior religious leaders of the Sunni Muslim world. The association followed Sultan Selim I’s conquest of the Mamluk Sultanate and control of Egypt, Mecca, and Medina.
The caliphate was a political and religious institution whose holder was traditionally seen as the successor to Muhammad in leading the Muslim community. Ottoman rulers had already used religious and imperial titles before 1517, including sultan and padishah, but the conquest of the Mamluk territories greatly strengthened their claim to universal Sunni leadership.
The exact story of a formal ceremony in which the last Abbasid caliph transferred the title to Selim is debated by historians and was emphasized more strongly in later Ottoman tradition. Even so, “caliph” is the canonical answer expected in a general-history quiz. Shah means a Persian monarch, emir is a ruler or commander, and sultan is an imperial title rather than specifically the religious office described here. The Ottoman caliphate was abolished by the Turkish Republic in 1924.