al-Mamun (786–833)

Ottoman ruler. He was the seventh caliph of the Abbasside Dynasty, from 813. He had defeated his brother, al-Amin, to gain the throne. Al-Mamun encouraged science and the arts. He died during a campaign against the Emperor Theophilus of Byzantium.

He was the second son of Harun al-Rashid, who divided the empire between him and his brother al-Amin. The latter was to rule Iraq and the West (and succeed al-Rashid as caliph) while al-Mamun was to rule Persia and the East, and succeed as caliph on al-Amin's death. Shortly after his accession, al-Amin tried to alter the succession in favour of his own son, which led to civil war. Al-Mamun owed his throne largely to Persian support and after his victory he allowed them self-government. Soon afterwards Persia became semi-independent under the Tahirid Dynasty. Al-Mamun was renowned for his generosity, his clemency, and his literary talent.

The civil war which led to al-Mamun's accession was symptomatic of the slow disintegration already apparent in the Abbasside empire.