Abū Isḥāq Muḥammad ibn Hārūn al-Rashīd, better known by his regnal name al-Muʿtaṣim biʾllāh, was the eighth Abbasid caliph, ruling from 833 until his death in 842. When al-Ma'mun died unexpectedly on campaign in August 833, al-Mu'tasim was thus well placed to succeed him, with the support of the powerful chief qādī, Ahmad ibn Abi Duwad, he continued to implement the rationalist Islamic doctrine of Mu'tazilism and implementing miḥna policy.