It may refer to his ruthless tactics, or perhaps it was used to intimidate his enemies, as it was common in history to adopt such names, an example for this is “Al Abbas” which means a “Lion that scares away other animals”.

[2] As narrated in many hadith, many believed that in the end times a great leader or mahdi would appear from the family of Muhammad, to which Ali belonged, who would deliver Islam from corrupt leadership.

During the reign of late Umayyad Caliph Hisham ibn Abd al-Malik this unrest led to a revolt in Kufa in southern Iraq, mainly by the town's slaves.

Shi'ites revolted in 736 and held the city until 740, led by Zayd ibn Ali, a grandson of Husayn and another member of the Banu Hashim.

During the last days of the Umayyad caliphate, Abu al-‘Abbās and his clan chose to begin their rebellion in Khurasān, an important, but remote military region comprising eastern Iran, southern parts of the modern Central Asian republics of Turkmenistan, Uzbekistan, Tajikistan, Kyrgyzstan and northern Afghanistan.

In Shi'ite works such as the al-Jafr faithful Muslims were told that the brutal civil war was the great conflict between good and evil.

[3] In early October 749 (132 AH), Abu al-'Abbās as-Saffāh's rebel army entered Kufa, a major Muslim center in Southern Iraq.

The latter was defeated in February 750 at a battle on the (Great) Zab river north of Baghdad, effectively ending the Umayyad caliphate, which had ruled since 661 AD.

[5] In one far-reaching, historic decision, as-Saffāh established Kufa as the new capital of the caliphate, ending the dominance of Damascus in the Islamic political world, and Iraq would now become the seat of 'Abbassid power for many centuries.

[citation needed] Equally revolutionary was as-Saffāh's reform of the army, which came to include non-Muslims and non-Arabs in sharp contrast to the Umayyads who refused any soldiers of either type.

The betrayal alienated as-Saffāh's Shi'a supporters, although the continued amity of other groups made Abbasid rule markedly more solvent than that of the Umayyads.

In July 751 AD, Tang and Abbasid forces met in the valley of the Talas River to vie for control over the Syr Darya region of central Asia.

Historians debate whether or not Chinese prisoners captured in the aftermath of the battle brought paper-making technology to the Middle East, where it eventually spread to Europe.

When the Tang capital was taken by rebels, all Chinese armies stationed in Central Asia were ordered back to China proper to crush the rebellion.

This agreement was supposed to resolve rivalries in the Abbasid family, but al-Mansur's right to accession was particularly challenged by his uncle Abdullah ibn Ali.