The term "Caliph" is taken from an Arabic term meaning "successor," or "representative." The term has also been translated as "deputy." A true Caliph is said to be the successor to the prophet Muhammad. In more modern parlance, a Caliph is the ruler of a community of Muslims who are governed by Shariah law. The authority of the Caliph as well as the origin of the title is a matter of dispute between Shia and Sunni Muslims.
The prophet Muhammad named no successor prior to his death in 632. Abu Akbar, who had been close to Muhammad, was chosen as the prophets successor, and is thereby generally considered to be the first true Caliph. The first four Caliphs, including Abu Akbar, were chosen by powerful Arabic clans; however shortly thereafter, disputes arose which led to the separation of Islam into Shia and Sunni sects.