Mahdi (Arabic mahdiy, “he who is guided aright”), the expected Muslim messiah, whose coming was prophesied in the 10th century. Some Muslims hold that the Mahdi has yet to appear; others believe that he has already been on earth but will return. Throughout Muslim history pretenders and fanatics have claimed to be the Mahdi. Of these the most famous was Ubayd Allah al-Mahdi, first caliph of the Fatimid dynasty, after whom the city of Mahdia was named. Another claimant to the title, Muhammad Ahmad, founded a short-lived empire in the eastern Sudan and in 1884-85 captured Khartoum, then defended by the British general Charles George Gordon.