Al-Musta'in, Abbasid caliph (born 836)

Abū al-ʿAbbās Aḥmad ibn Muḥammad ibn Muḥammad al-Mustaʿīn bi-ʾllāh, better known by his regnal title al-Mustaʿīn was the Abbasid caliph from 862 to 866, during the "Anarchy at Samarra". After the death of previous Caliph, al-Muntasir, the Turkic military leaders held a council to select his successor. They were not willing to have al-Mu'tazz or his brothers; so they elected Ahmad ibn Muhammad, a nephew of al-Mutawakkil, who took the regnal name al-Mustaʿīn bi-ʾllāh.