Abu Isḥaq Muḥammad ibn Harun al-Rashid, better known by his regnal name al-Muʿtaṣim biʾllāh, was the eighth Abbasid caliph, ruling from 833 until his death in 842.

A younger son of Caliph Harun al-Rashid, he rose to prominence through his formation of a private army composed predominantly of Turkic slave-soldiers.