ʿAbd Allāh, in full ʿabd Allāh Ibn Muḥammad At-taʿīʾishī, also called ʿabdullahi (born 1846, Sudan—died Nov. 24, 1899, Kordofan), political and religious leader who succeeded Muḥammad Aḥmad (al-Mahdī) as head of a religious movement and state within the Sudan.
ʿAbd Allāh followed his family’s vocation for religion. In about 1880 he became a disciple of Muḥammad Aḥmad, who announced that he had a divine mission, became known as al-Mahdī, and appointed ʿAbd Allāh a caliph (khalīfah). When al-Mahdī died in 1885, ʿAbd Allāh became leader of the Mahdist movement. His first concern was to establish his authority on a firm basis. Al-Mahdī had clearly designated him as successor, but the Ashraf, a portion of al-Mahdī’s supporters, tried to reverse this decision. By promptly securing control of the vital administrative positions in the movement and obtaining the support of the most religiously sincere group of al-Mahdī’s followers, ʿAbd Allāh neutralized this opposition. ʿAbd Allāh could not claim the same religious inspiration as had al-Mahdī, but, by announcing that he received divine instruction through al-Mahdī, he tried to assume as much of the aura as was possible.
ʿAbd Allāh believed he could best control the disparate elements that supported him by maintaining the expansionist momentum begun by al-Mahdī. He launched attacks against the Ethiopians and began an invasion of Egypt. But ʿAbd Allāh had greatly overestimated the support his forces would receive from the Egyptian peasantry and underestimated the potency of the Anglo-Egyptian military forces, and in 1889 his troops suffered a crushing defeat in Egypt.
A feared Anglo-Egyptian advance up the Nile did not materialize. Instead ʿAbd Allāh suffered famine and military defeats in the eastern Sudan. The most serious challenge to his authority came from a revolt of the Ashraf in November 1891, but he kept this from reaching extensive proportions and reduced his opponents to political impotence.
During the next four years, ʿAbd Allāh ruled securely and was able to consolidate his authority. The famine and the expense of large-scale military campaigns came to an end. ʿAbd Allāh modified his administrative policies, making them more acceptable to the people. Taxation became less burdensome. ʿAbd Allāh created a new military corps, the mulazimiyah, of whose loyalty he felt confident.
But in 1896 Anglo-Egyptian forces began their reconquest of the Sudan. Although ʿAbd Allāh resisted for almost two years, he could not prevail against British machine guns. In September 1898 he was forced to flee his capital, Omdurman, but he remained at large with a considerable army. Many Egyptians and Sudanese resented the Condominium Agreement of January 1899, by which the Sudan became almost a British protectorate, and ʿAbd Allāh hoped to rally support. But on Nov. 24, 1899, a British force engaged the Mahdist remnants, and ʿAbd Allāh died in the fighting.