Khalifah or vicegerent is one who exercises the authority delegated to him by his principal, and does so in the capacity of his deputy and agent. This term has been used in the Quran with reference to man: 'Just think when your Lord said to the angels: Lo! I am about to place a vicegerent on earth...' (2:30). At certain places in the Qur'an, khulafa (pl.) also means (a) people with power to mobilize all that is on earth (27:62); (b) successors or inheritors who will inherit the earth and succeed one after another (24:55; 38:26). In the political history of Islam, khalifa became the title of the successors of the Prophet Muhammad (S.A.W.), notably the first four Rightly-Guided Caliphs known as al-Khulafa al-Rashidun (11-35 A.H., 632-655 C.E.). With the establishment of the Umayyad hereditary rule immediately after this, the institution of the Caliphate changed into monarchy. Yet the rulers called themselves Caliphs. Formally the institution of the Caliphate came to an end in 1924 C.E. when Kamal Ataturk of Turkey arbitrarily declared its abolition.