Musa was born (according to one account, in c. 746)[1] to Isa ibn Musa, a member of the Banu al-Abbas who served as a long-running governor of Kufa during the first years of the Abbasid Caliphate.[2] An extended relation of the Abbasid dynasty, Musa was a great-nephew of its first two caliphs al-Saffah (r. 750–754) and al-Mansur (r. 754–775);[3] he was also connected to the ruling line by his marriage to Ulayya, daughter of the third caliph al-Mahdi.[4]