Caliph is a term used to describe the chief ruler of the Muslim community, serving as a successor to the Islamic prophet Muhammad. Literally meaning “successor,” or “next in line,” the caliph holds political, military, and administrative power over the Islamic world. Caliphs have at times also been referred to as “Emir-ul Momineen,” or “Commander of the Faithful.”

The first caliph, Muhammad’s father-in-law Abu Bakr, was elected by a group of Muhammad’s followers directly after the prophet’s death in 632 CE. A separate group of early Muslims opposed the selection of Abu Bakr, instead favoring Muhammad’s cousin and son-in-law, Ali ibn Abi Talib—who eventually served as the fourth caliph. These debating camps evolved into the Sunni and Shiite sects, respectively.

Sunni leaders throughout the centuries have adopted the titles “Caliph” and “Emir-ul Momineen.” Taliban founder and leader Mullah Omar, for example, appointed himself Emir-ul Momineen in 1994—gaining the fealty of top al-Qaeda leaders including Osama bin Laden. In June 2014, then-ISIS spokesman Abu Mohammad al-Adnani called Abu Bakr al-Baghdadi “Caliph Ibrahim”—designating him the leader of “Muslims everywhere” and demanding unsuccessfully the allegiance of all Muslims.