Al-Musta'in

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 period known as the "Anarchy at Samarra". Following the death of caliph al-Muntasir, the Turkic military leaders bypassed the claims of al-Mu'tazz and his brothers and selected al-Mustaʿīn, a nephew of al-Mutawakkil, as caliph.