Musa ibn Ja'far al-Kazim was a descendant of the Islamic prophet Muhammad and the seventh Imam in Twelver Shia Islam, succeeding his father Ja'far al-Sadiq. Born around 745 in Medina, al-Kazim spent the first twenty years of his life under the care and guidance of his father. This period coincided with the struggle between the Abbasids and the Umayyads. Following Ja'far al-Sadiq's death, some of his followers recognized his other son Isma'il ibn Ja'far as the next Imam, separating from the mainstream Shia Islam and forming the Isma'ili sect. However, Musa al-Kazim attracted the largest following, and his followers ultimately became what developed into Twelver Shi'ism, the largest branch of Shia Islam. His Imamate continued through the reigns of al-Mansur, al-Mahdi, al-Hadi, and Harun al-Rashid. Like his predecessors, al-Kazim generally avoided politics and devoted himself to religious teachings. He was nevertheless tightly restricted by the Abbasid caliphs and spent much of his adult life in their prisons. To counter these restrictions, he established a network of representatives to organize the affairs of his followers across the Abbasid Empire.