Islāmic caliph (reigned 749–754), first of the ʿAbbāsid dynasty, which was to rule over eastern Islām for approximately the next 500 years. The ʿAbbāsids were descended from an uncle of Muḥammad and were cousins to the ruling Umayyad Dynasty. The Umayyads were weakened by decadence and an unclear line of succession, and they enjoyed little popular support, prompting the ʿAbbāsids to declare open revolt in 747. When Abū al-ʿAbbās assumed the caliphate in 749, he began a campaign of extermination against the Umayyads, the ʿAlids, other ʿAbbāsid leaders who had become too popular, and all other claimants to power. He named himself as-Saffāḥ, “the blood-shedder,” because of his savage attacks. He established a firm legal and dynastic base for the ʿAbbāsids. His successor moved the caliphate to Baghdad.