Abdallah ibn Ali

Abdallah ibn al-Abbas (ca. 712 – 764 CE) was a member of the Abbasid dynasty, who played a leading role in its rise to power during the Abbasid Revolution. As governor of Syria, he consolidated Abbasid control over the province, eliminating the remnants of the Umayyad dynasty and suppressing pro-Umayyad uprisings. After the death of his nephew and first Abbasid Caliph, al-Saffah, in 754, he launched a bid for the caliphal title against al-Saffah's brother, al-Mansur, but was defeated and imprisoned. He was killed in 764.

Abdallah was a member of the Abbasid family, and uncle to the first two Abbasid caliphs, al-Saffah (reigned 749–754) and al-Mansur (r. 754–775).

By early 749, the anti-Umayyad uprising that had begun under Abu Muslim in Khurasan had prevailed in the eastern lands of the Caliphate, and the Khurasani armies swept west across Persia to the borders of Iraq. In October 749, al-Saffah was proclaimed Caliph at Kufa, and quickly gained the acceptance of Abu Muslim and the Kufans, thereby forestalling an Alid bid for control of the Revolution. To cement Abbasid control, al-Saffah now appointed members of his own family to command the armies: his brother, the future al-Mansur, was sent to lead the Siege of Wasit, while Abdallah was sent to confront the Umayyad caliph Marwan II in the Jazira.

Thus Abdallah held the supreme command in the decisive Battle of the Zab, where the Abbasid forces defeated the last Umayyad Caliph, Marwan II (r. 744–750), and led the pursuit of the latter, first to Syria, where he captured the Umayyad capital, Damascus, and then to Palestine, forcing Marwan to flee to Egypt. His brother Salih followed Marwan to Egypt, where the Umayyad ruler was captured and executed.

...
Wikipedia