Al Mansur (r. 754-775 C.E.) was the Abbasid Caliph who founded Baghdad in 762.
al-Mansur was concerned with the solidity of his regime after the death of his brother, al-'Abbas. In 755, he arranged the murder of Abu Muslim, the general who had lead the forces of al-'Abbas to victory over the Umayyads in the third civil war. He undertook to make certain that the 'Abbasid family was supreme in state affairs, and that its sovereignty over the Caliphate would go unquestioned.
He claimed, as earlier Umayyad caliphs had done, to hold religious and secular authority. This further alienated Shi'ite Moslems who had, during the reign of al-'Abbas, wanted the Imam to be made Caliph.
During his reign, literature and scholarly work in the Islamic world began to emerge in full force, supported by new Abbasid tolerances for Persians and other groups suppressed by the Umayyads. Although the Umayyad caliph Hisham had adopted Persian court practices, it was not until al-Mansur's reign that Persian literature and scholarship came to true appreciation in the Islamic world. The emergence of Shu'ubiya among Persian scholars occurred during the reign of al-Mansur as a result of loosened censorship over Persian nationalism. Shu'ubiya was a literary movement among Persians expressing their belief that Persian art and culture was superior to that of the Arabs; the movement, served to catalyze the emergence of Arab-Persian dialogues in the eight century.
Perhaps more importantly than the emergence of Persian scholarship was the conversion of many non-Arabs to Islam. The Umayyads - who actively tried to discourage conversion in order to continue the collection of the jizya, or the tax on non-Moslems. The inclusiveness of the Abbasid regime, and that of al-Mansur, saw the expansion of Islam among its territory; in 750, roughly 8% of residents in the Caliphate were Moslems. This would double to 15% by the end of al-Mansur's reign.
al-Mansur died in 775, and was suceeded by al-Mahdi, his son.