(Arabic: “Helper”), follower of al-Mahdī (Mahdī, al-) (Muḥammad Ahmad ibn as-Sayyid ʿAbd Allāh) or of his successor or descendants. Ansar is an old term applied to some of the companions of the prophet Muḥammad; it was revived for the followers and descendants of al-Mahdī, the Sudanese who in the late 19th century deemed himself a new prophet divinely appointed to restore Islām.

The Mahdists rose to prominence during the successful Sudanese wars and theocratic regime commanded by al-Mahdī from 1881 until his death in June 1885. His disciple ʿAbd Allāh succeeded to the temporal rule. But, following initial victories, his forces were gradually hunted down by Anglo-Egyptian armies and almost entirely destroyed in the Battle of Omdurman (Omdurman, Battle of) (q.v.; Sept. 2, 1898); he himself was killed in the final Battle of Umm Dibaykarat (Nov. 24, 1899). Leadership of the movement then passed to the Mahdī's son ʿAbd ar-Raḥmān (d. 1959), who, in the face of Anglo-Egyptian rule, sought to make the Ansar into a religious and political force. In 1959 he was succeeded as imam of the Ansar by his son Siddiq (d. 1961), who in turn was succeeded by a member of another branch of the family, Hadi ibn ʿAbd ar-Raḥmān. When the latter was killed fighting the leftist revolutionary government of The Sudan in 1970, most members of the Mahdī family fled into exile.