MAHDÍ. i.e., “he who is guided aright,” the third caliph of the house of *Abbâs (see Mohammedan Empire). The name of Mahdi is also that which the Shi'ite Mohammedans give to their Messiah, the last of the Imâms of the house of Αli. It was under the name of al-Mahdi that Mokhtâr proclaimed t Ali ’ s son Mohammed as the opponent of the caliph'Abd al-Malik, and, according to Shahrastani, p. Ill, the doctrine of the Mahdi, the hidden deliverer who is one day to appear and fill the oppressed world with righteousness, first arose in connexion with a wild notion that this Mohammed had not died but lived concealed at Mount Radwâ, near Mecca, guarded by a lion and a panther. The hidden Imâm of the common Shi'ites is, however, the twelfth Imâm, Mohammed Abu’l-Kâsim, who disappeared mysteriously 879 A.D. The belief in the appearance of the Mahdi readily lent itself to imposture. Of the many prétendants to this dignity known in all periods of Moslem history down to the present day the most famous was the first caliph of the Fatimite dynasty in North Africa, 'Obaid-allâh al-Mahdi, who reigned 909-934 A.D. From him was named the capital of the dynasty, the once mighty city of Mahdiya, the port and entrepot of Kairawân (see Mohammedan Empire under the reign of Moktadir). Another great historical movement, headed by a leader who proclaimed himself the Mahdi (Mohammed ibn Abdallah ibn Tûmrut), was that of the Almohades (q.v.).