Al-Ma'mun
Abū al-ʿAbbās Abd Allāh ibn Hārūn al-Maʾmūn (Arabic: أبو العباس عبد الله بن هارون الرشيد, romanized: Abū al-ʿAbbās ʿAbd Allāh ibn Hārūn ar-Rashīd; 14 September 786 – 9 August 833), better known by his regnal name al-Ma'mun (Arabic: المأمون, lit. 'the Reliable'), was the seventh Abbasid caliph, who reigned from 813 until his death in 833. His leadership was marked by the power and prosperity of the Abbasid Caliphate, al-Ma'mun promoted the Graeco-Arabic translation movement, the flowering of learning and the sciences in Baghdad, and the publishing of al-Khwarizmi's book now known as "Algebra", making him one of the most important caliphs in the Islamic Golden Age.