MAHDI (Arab. " he who is guided aright ")  , a title assumed by the third Abbasid caliph (see CALIPHATE: Abbasids, § 3) . According to Moslem traditionists Mahomet declared that one of his descendants, the imam of God, who would fill the earth with equity and justice, would bear the name of al-mandi . The Sunnis hold that this mandi has not yet appeared . The name of mandi is also given by the Shiite Mahommedans to the last of the imams of the house of `Ali . It was under the name of al-mandi that Mokhtar proclaimed 'Ali's son Mahommed as the opponent of the caliph Abdalmalik, and, according to Shahrastani, the doctrine of the mandi, the hidden deliverer who is one day to appear and fill the oppressed world with righteousness, first arose in connexion with a belief that this Mahommed had not died but lived concealed at Mount Radwa, near Mecca, guarded by a lion and a panther . The hidden imam of the common Shiites is, however, the twelfth imam, Mahommed Abu'l-Qasim, who disappeared mysteriously in 879 . The belief in the appearance of the mandi readily lent itself to imposture . Of the many pretenders to this dignity known in all periods of Moslem history the most famous was the first caliph of the Fatimite dynasty in North Africa, `Obaidallah al-Mandi, who reigned 909-933 . After him was named the first capital of the dynasty, the once important city of Mandia (q.v.) . Another great historical movement, headed by a leader who proclaimed himself the mandi (Mahommed ibn Abdallah ibn Tumart), was that of the Almohades (q.v.) . In 1881 Mahommed Ahmed ibn Seyyid Abdullah (q.v.), a Dongolese, proclaimed himself al-mandi and founded in the eastern Sudan the short-lived empire overthrown by an Anglo-Egyptian force at the battle of Omdurman in 1898 . Con-currently with the claim of Mahommed Ahmed to be the mandi the same title was claimed by, or for, the head of the Senussites, a confraternity powerful in many regions of North Africa .