Mansur was the son of al-Mahdi and his mother was al-Bahtariyah, the noble-born daughter of the Persian rebel,[1] Masmughan of Damavand,[2] against whom Mahdi was first sent to Khurasan.
[2] She bore al-Mahdi a son named for his grandfather, Mansur, and two daughters, Sulaimah and Aliyah.
[1] His father, nominated his two elder sons; Musa al-Hadi and Harun al-Rashid as heirs.
He remained in office until al-Amin reappointed Sulayman to govern Syria around 809–810 in response to unrest in Damascus emanating from the theft of a prized crystal pitcher from the Umayyad Mosque by the incumbent governor, Sulayman's nephew Mansur.
He had total ten half-siblings and he had two full sisters named Aliyah and Sulaimah.