Al-Ma'mun

Abū Al-Abbas Abdullāh al-Maʾmūn ibn Harūn (also spelled Almamon, Al-Maymun, Al-Ma’moon, and el-Mâmoûn; 13 September 786 – 9 August 833) was an Abbasid caliph. He reigned from 813 until his death in 833.
Al-Ma’mun was born on 13 September 786 AD in Baghdad. His father was Harun al-Rashid, who was an Abbasid caliph. He was a member of the third dynasty of the descendants of Muhammad who were caliphs of Islam. While his father ruled, al-Ma’mun was the governor of Khorasan. After al-Ma’mun was born his father had another son named al-Amin. Before his father died he announced that al-Amin would be the new caliph and al-Ma’mun would continue to be the governor of Khorasan even though al-Ma’mun was older. When Harun al-Rashid died and al-Amin became the caliph, he took away al-Ma’mun's ability to inherit the throne after he died. The two brothers went to war against each other. Al-Ma’mun defeated al-Amin. He cut off al-Amin's head. Since al-Amin had no other heir to the throne, al-Ma’mun became the new caliph.
During his reign al-Ma’mun tried to reunite Sunnis and Shiites. These are the two main brances of Islam that have different beliefs on who should lead Islam. Al-Ma’mun opened many learning centers in his empire. One big one was in Baghdad, which was called the House of Wisdom. Many other libraries and schools were built all over the empire. He was also a big sponsor of philosophy and astronomy.
He had one wife who he tried to divorce. However, his wife got a powerful judge who refused to allow the divorce. He had no children and no heirs with this wife. Instead, he chose another woman to provide an heir.
Al-Ma’mun died on August 9, 833. He remained caliph until his death.