Any of the successors of Muhammad (Mohammed) as rulers and religious leaders of the Muslim community, the most powerful being those of the Umayyad and 'Abbasid dynasties. A caliphate is the Islamic empire ruled by a caliph. When Muhammad died (June 8, 632), Abu Bakr succeeded to his political and administrative functions as khalifah rasul Allah, successor of the Messenger of God but it was probably under 'Umar ibn al-Khattab, the second caliph, that the term caliph came into use as a title of the civil and religious head of the Muslim state. Abu Bakr and his three immediate successors are known as the "perfect" caliphs. There were then 14 Umayyad caliphs and 38 'Abbasid caliphs whose dynasty fell to the Mongols in 1258. There were titular caliphs from 1258-1517 when the last caliph was captured by the Ottoman sultan Selim I. The Ottoman sultans then claimed the title and used it until it was abolished by the Turkish Republic in 1924.