Al-Ma'mun

Born in September 786, Abd Allāh ibn Hārūn became the seventh Abbasid caliph in 813 after a civil war against his half-brother al-Amin. He spent much of his reign on military campaigns, navigating cycles of war and diplomacy with the Byzantine Empire while consolidating power at home. But his legacy rests on what he built in Baghdad: he championed the Graeco-Arabic translation movement, presided over a flourishing of science and learning, and oversaw the publication of al-Khwarizmi's work on algebra. His commitment to Mu'tazilism - a rationalist strain of Islamic theology - eventually turned coercive; he imprisoned the Sunni imam Ahmad ibn Hanbal in an episode known as the mihna. He died in August 833, leaving the caliphate at the height of its intellectual power and reach.