Abū Jaʿfar Abdullāh al-Maʾmūn ibn Harūn ( also spelled Almamon , Al-Maymun , Al-Ma 'm oon , Mahmoun and el-Mâmoûn ( ) ( September 786 -- 9 August 833 ) was an Abbasid caliph who reigned from 813 until his death in 833 .
Abū Jaʿfar Abdullāh al-Maʾmūn ibn Harūn ( also spelled Almamon , Al-Maymun , Al-Ma 'm oon , and el-Mâmoûn ; 13 September 786 -- 9 August 833 ) was an Abbasid caliph . He reigned from 813 until his death in 833 .