The word "caliph" refers to the successor to Muhammad as the leader of the Muslim community. The term was held by the leader of the large Muslim empires that thrived in the Middle East after the death of Muhammad.
When the Prophet Muhammad died in 632 CE, Bakr took over as the spiritual and administrative leader of the Muslim community. Eventually, the caliphate evolved from an elected position to more of a dynastic one. The first clan to dominate the office was the Umayyad clan, which gave way to the Abbasid clan. Other claimants to the title, such as the Fatimid dynasty, also claimed the title from time to time. Eventually, the remnants of the Abbasid dynasty transferred the title to the Ottoman sultan in 1517. The Turks abolished the office in 1923.