Abu Muslim Abd al-Rahman ibn Muslim al-Khorasani or al-Khurasani (Arabic: أبو مسلم عبد الرحمن بن مسلم الخراساني born 718-19 or 723-27, died in 755), born Behzādān Pūr-i Wandād Hormozd (Persian: بهزادان پور ونداد هرمزد), was a Persian general in service of the Abbasid dynasty, who led the Abbasid Revolution that toppled the Umayyad dynasty.
Abu Muslim al-Khorasani
Unknown, possibly Behzadan, or Ibrahim
718-19 or 723-27
|Died||755 (aged 37)|
|Known for||Abbasid Rebellion|
|Political party||Abbasid Commander in chief|
|Parent(s)||Vandad Hurmuz (father)|
According to the Encyclopedia Iranica, "sources differ regarding his original name and his origin. Some make him a descendant of Gōdarz and of the vizier Bozorgmehr and call him Ebrāhīm; some name him Behzādān, son of Vendād Hormoz; and others relate him to the ʿAbbasids or to ʿAlī’s family. These suggestions are all doubtful". He was possibly of Persian origin and was the mowlā of an Arab tribe. Other sources refer to him as a Yaminite, a Kurd, an Arab or even a descendant of the ancient Iranian aristocracy. It is also said that he was born in Sar-e Pol Province of present-day Afghanistan to a Tajik family.
There was an Arab by the name Sharik ibn Shaikh al-Mahri in Bukhara, who wanted to spread Shia Islam firmly and oppose anyone against him. Soon, he got the support of several local rulers and many local people.
When this news reached Abu Muslim, he along with Ziyad ibn Salih came there to find out the details, and soon they got involved in a fight. Abu Muslim fought Sharik ibn Shaikh al-Mahri and his Shiite supporters for thirty-seven days with no victory, everyday Abu Muslim's side was losing soldiers and several taken as prisoners. After that, all of a sudden Sharik ibn Shaikh al-Mahri died, and his supporters started to crumble but were still hostile. The rebellion was eventually crushed and most of the Shia supporters were hanged. 
Abu Muslim observed the revolt in Kufa in 736 tacitly. With the death of the Umayyad Caliph Hisham ibn Abd al-Malik in 743, the Islamic world was launched into civil war. Abu Muslim was sent to Khorasan by the Abbasids initially as a propagandist and then to revolt on their behalf. He took Merv in December 747 (or January 748), defeating the Umayyad governor Nasr ibn Sayyar, as well as Shayban al-Khariji, a Kharijite aspirant to the caliphate. He became the de facto governor of Khorasan, and gained fame as a general in the late 740s in defeating the rebellion of Bihafarid, the leader of a syncretic Persian sect that were Mazdaism. Abu Muslim received support in suppressing the rebellion both from purist Muslims and Zoroastrians. In 750, Abu Muslim became leader of the Abbasid army and defeated the Umayyads at Battle of the Zab. Abu Muslim stormed Damascus, the capital of the Umayyad caliphate, later that year.
His heroic role in the revolution and military skill, along with his conciliatory politics toward Shia, Sunnis, Zoroastrians, Jews, and Christians, made him extremely popular among the people. Although it appears that Abu al-'Abbas al-Saffah trusted him in general, he was wary of his power, limiting his entourage to 500 men upon his arrival to Iraq on his way to Hajj in 754. Abu al-'Abbas's brother, al-Mansur (r. 754-775), advised al-Saffah on more than one occasion to have Abu Muslim killed, fearing his rising influence and popularity. It seems that this dislike was mutual, with Abu Muslim aspiring to more power and looking down in disdain on al-Mansur, feeling al-Mansur owed Abu Muslim for his position. When the new caliph's uncle, Abdullah ibn Ali rebelled, Abu Muslim was requested by al-Mansur to crush this rebellion, which he did, and Abdullah was given to his nephew as a prisoner. Abdullah was ultimately executed.
Relations deteriorated quickly when al-Mansur sent an agent to inventorize the spoils of war, and then appointed Abu Muslim governor of Syria and Egypt, outside his powerbase. After an increasingly acrimonious correspondence between Abu Muslim and al-Mansur, Abu Muslim feared he was going to be killed if he appeared in the presence of the Caliph. He later changed his mind and decided to appear in his presence due to a combination of perceived disobedience, al-Mansur's promise to keep him as governor of Khorasan, and the assurances of some of his close aides, some of whom were bribed by al-Mansur. He went to Iraq to meet al-Mansur in al-Mada'in in 755. Al-Mansur proceeded to enumerate his grievances against Abu Muslim, who kept reminding the Caliph of his efforts to enthrone him. Against Abu Muslim were also charges of being a zindiq or heretic. al-Mansur then signaled five of his guards behind a portico to kill him. Abu Muslim's mutilated body was thrown in the river Tigris, and his commanders were bribed to acquiesce to the murder.
His murder was not well received by the residents of Khorasan, and there was resentment and rebellion among the population over the brutal methods used by Al-Mansur. He became a legendary figure for many in Persia, and several Persian heretics started revolts claiming he had not died and would return; the latter included his own propagandist Ishaq al-Turk, the Zoroastrian cleric Sunpadh in Nishapur, the Abu Muslimiyya subsect of the Kaysanites Shia, and al-Muqanna in Khorasan. Even Babak claimed descent from him.
At least three epic romances were written about him: