In Arabic, caliph means "a successor to the prophet". This is what leaders of the Islamic faith came to be called. Their rule is called a caliphate.
Some of the early leaders of the Muslim community following Muhammad's (570–632) death called themselves "Khalifat Allah", meaning representative of God. But the other title of "Khalifat rasul Allah", meaning the successor to the prophet of God, became the common title. Some academics write the term as Khalīf.
Caliphs were often also called Amīr al-Mu'minīn (أمير المؤمنين), leader of the Muslims. This title has since been shortened to "emir". It is also found as a personal name in some countries.
After the first four caliphs (Abu Bakr, Umar ibn al-Khattab, Uthman ibn Affan, and Ali ibn Abi Talib), the title was used by the Umayyads, the Abbasids, and the Ottomans, as well as by other dynasties in Southern Pakistan, Spain, Northern Africa, and Egypt. Most historical Muslim rulers simply titled themselves sultans or emirs, and the caliph himself often had very little real authority. The title was not used after the Republic of Turkey abolished the Ottoman caliphate in 1924.