A caliph is someone claiming authority over Muslims, and the area ruled by a caliph is called a caliphate. The word caliph comes from the Arabic "khalifa," which means a successor. The first caliphs were the heirs to Muhammad, the founder of Islam. The caliphs were not prophets with theological authority, but they were heirs to Muhammad's political authority and shaped Islam in many ways.

Varying Importance of the Caliphate

The meaning of the caliphate changed greatly through time. At the beginning, the caliphate was an important religious office as Muslims tried to continue to follow the "straight path," or sharia, after the death of Muhammad. The caliph had religious credibility because he was elected by the faithful, and his precedents would prove critical to the future of Islam. This changed with the emergence of political dynasties, when the office of the caliphate was more about power than piety.

The Rightly Guided Caliphs

Abu Bakr was the first caliph, succeeding Muhammad in 632. Much like George Washington with the American presidency, Abu Bakr set precedents that remained forever. The most important of these was that Abu Bakr declined to take the office of prophet, making the caliph an imitator of Muhammad rather than someone with Muhammad's authority. The first four caliphs — Abu Bakr, Umar, Uthman and Ali — were all known for their exceptional piety and dedication to the "umma," or Muslim community.

The Caliphate and the Sunni-Shia Divide

This period of the caliphate caused the greatest schism in the history of Islam, and the divide exists to this day. Sunni Muslims believe Abu Bakr was the correct choice for first caliph, trusting the righteousness of the first community. Shia Muslims, on the other hand, believe that Ali should have been the first, rather than the fourth, caliph because Muhammad had designated him as successor. Shias believe legitimacy follows the family line of Muhammad — Ali was Muhammad's cousin and was married to his daughter, Fatima.

The Dynasties

After Ali's death in 661, a political dynasty named the Umayyads rose to power. At this point the caliphate was less concerned about Islamic legitimacy and more concerned with maintaining an empire that stretched from North Africa to Persia. The Umayyads were followed by other notable dynasties such as the Abbasid Dynasty and the Fatamid Dynasty. Eventually the center of power shifted from the Arabs to the Turks, and the caliphate was transferred to the Ottoman Empire in the 15th century.

The End of the Caliphate

The caliphate ended with the Ottoman loss in WWI, and much of the Ottoman Empire was divided among the French and British. Nearly a century has passed since anyone claimed to be a caliph, but many Muslim groups desire a return to the caliphate. One of these groups is Hizb ut-Tahrir, which rallied 100,000 pro-caliphate Muslims in Indonesia in 2007. Al Qaida also desires a return to the caliphate, according to Al Qaida expert Lawrence Wright.