Abu Mansur al-Faḍl ibn Ahmad al-Mustazhir (; 1092 – 29 August 1135) better known by his regnal name Al-Mustarshid Billah () was the Abbasid caliph in Baghdad from 1118 to 1135. He was son of his predecessor, caliph al-Mustazhir. He succeeded his father in the year 1118 as the Abbasid caliph. He was also an Arabic poet. Biography Al-Mustarshid was born in 1092. He was son of Caliph Al-Mustazhir. His mother was a Slavic concubine named Lubanah. She was from Baghdad. His was named Al-Fadl by his father. His full name was Al-Fadl ibn Ahmad al-Mustazhir and his Kunya was Abu Mansur. After the death of his father in 1135, he succeeded him as Caliph. Al-Mustarshid achieved more independence as a ruler while the Seljuk sultan Mahmud II was engaged in war in the East. In 1122, al-Mustarshid deposed and imprisoned his vizier Amid al-dawla Jalal al-Din Hasan ibn Ali. Mahmud II then imposed Ahmad ibn Nizam al-Mulk as his vizier. In 1123, Banu Mazyad general Dubais ibn Sadaqah tried to take advantage of the momentary lack of power and, after plundering Bosra, attacked Baghdad together with a young brother of the sultan, Ghiyath ad-Din Mas’ud (known as Mas'ud) He was however crushed by an army under Zengi and Ahmad ibn Nizam al-Mulk. During the same year, al-Mustarshid removed Ahmad ibn Nizam al-Mulk as his vizier. In 1125, it was the time of al-Mustarshid to rebel. He sent an army to take Wasit but was defeated near Baghdad and imprisoned in his palace the next year. After the death of Mahmud II, a civil war broke out in the Seljuk western territories. Zengi was recalled to the east by certain rebel members, stimulated by the caliph and Dubais. Zengi was beaten and fled. The caliph pursued him to Mosul, and besieged him there but without success for three months. It was nonetheless a milestone in the revival of the military power of the caliphate. Zengi now resumed operations in Syria and, in 1134, laid siege to Damascus, but was induced, partly by the bravery of the enemy, partly at the instance of the caliph, to whom Zengi had made some concession in the public prayers, to relinquish the attempt. Recalled again by troubles in the east, he was unable to do much against the Crusaders till after al-Mustarshid's death. Not long after the siege of Damascus, al-Mustarshid launched a military