The word "caliph" -- "khalifah" in Arabic -- means " successor" and refers historically to the succession of leadership in the Islamic world after the death of the Prophet Muhammad. The issue of who would serve as Caliph -- as the political head of the Muslim empire, or Caliphate --- proved to be divisive for the followers of Islam, creating a deep schism within the community. The Caliphate effectively ended in the 13th century, but even today, some Muslim groups seek its re-establishment.
The Prophet Muhammad, regarded by Muslims as God's messenger and the founder of Islam, died in Medina, Saudi Arabia in A.D. 632. At this time, the Islamic world was growing, as Muslim armies spread out from the Arabian peninsula to claim more territories. The political stability of the expanding Islamic realm was shaky, however, because of the unresolved issue of the Prophet's successor. Muhammad himself had left no instructions for the succession; and after his death, a number of Arab tribes sought to withdraw from the Muslim federation, because their loyalty was to Muhammad himself and not to the government as such. The Muslim community ultimately selected a successor in Muhammad's father-in-law, Abu Bakr, who became the first Caliph. Bakr, and the three Caliphs who followed him, are considered the "Patriarchal Caliphs" who ruled during Islam's golden age of imperial expansion and growing strength.
The First Caliphs
As Islam's first Caliph, Abu Bakr immediately began consolidating power and battling those groups who sought to leave the Muslim federation. Within two years, he had defeated the apostates, shaping the Arabian peninsula into a stable Islamic state. Bakr died in 634, just two years after coming into power. He was succeeded by the second Caliph, Umar ibn al-Khattab, who ruled until 644. During Umar's time as Caliph, Islam expanded, conquering Iraq, Syria, Jordan and Palestine, and launching raids into Persia and North Africa. Umar's importance as Caliph was not only military: he also began building the political and financial structures of the burgeoning Islamic empire, and established the Muslim calendar.
Uthman and Ali
Umar was succeeded as Caliph by Uthman, who reigned from 644 to 656. Uthman was chosen over Ali, the son-in-law of the Prophet. Uthman was unpopular with some Muslims, but nevertheless accomplished a great deal as Caliph: he conquered North Africa, and ordered the creation of a definitive written version of Islam's holy text, the Quran. Uthman was killed by his own people when he tried to use the army to suppress protest riots in Medina.
The Sunni-Shiite Split
Ali finally became Caliph after Uthman's death in 656. Ali's Caliphate was troubled from the start: he was accused by his detractors of not pursuing Uthman's killers and of purging Uthman's supporters from the government. Ali battled rival clans and rebel factions within the empire during much of his rule. He was assassinated in 661. The ongoing issue of succession, culminating in Ali's Caliphate, is at the heart of a deep schism within Islam, namely the Sunni-Shiite split. In Sunni Islam, the Caliph is elected by the Muslim community. Shiite Muslims regard Ali, husband of the Prophet's daughter Fatimah, as a saintly figure, second only to Muhammad himself and the Prophet's rightful heir. For Shiites, Ali was the first imam and, as Britannica observes, "the ancestor of all subsequent imams." For Shiites, as "The Economist" points out, the choosing of a Caliph is "a sacred mandate" -- the Caliph is selected by God from the ancestors of Ali.
In the century after the death of Ali, a series of Caliphs ruled the Islamic empire, all of whom were connected by clan -- the Umayyad clan -- to Uthma. The period from 661 to 750 is referred to as the Umayyad caliphate, during which time the Caliphs built the Dome of the Rock in Jerusalem and conquered North Africa and southern Spain. The Umayyads were overthrown by the Abbasids in 750, paving the way for the Abbasid caliphate and a dynasty that would endure until the Mogol invasion of Baghdad in the 13th century. The last Islamic caliphate existed under the Ottoman dynasty, beginning in the late 13th century and lasting until its dissolution by Turkey in 1924. Today, some Muslim political groups, including the Muslim Brotherhood, envision and strive toward the return of the caliphate.