The Shi‘a appeared on the historical stage in the formative period of Islam with their own distinct identity and ideas on religious authority and leadership revolving around the sanctity of the Prophet Muhammad's family or the ahl al-bayt. Soon after the tragedy of Karbala’ where al-Husayn b. ‘Ali, the Shi‘i imam and the Prophet's grandson, and his small band of companions were massacred by an Umayyad army in 61/680, the Shi‘a themselves split into different groups, each one recognising a different line of ‘Alids, descendants of ‘Ali b. Abi Talib (d. 40/661), the Prophet's cousin, son-in-law and the first Shi‘i imam, or other members of the then broadly defined ahl al-bayt, as their spiritual leaders or imams.

Subsequently, Shi‘ism evolved in terms of two main branches, designated as the Kaysaniyya and the Imamiyya, each comprised of a number of sects and splinter groups. However, both of these Shi‘i branches represented minority positions within the Islamic community compared to groups later collectively designated as Sunnis. The Kaysanis, representing the politically active wing of Shi‘ism, were gradually absorbed into the Abbasid movement that succeeded in supplanting the Umayyads and installing the Abbasids to the caliphate in 132/750. It was in the aftermath of the establishment of Abbasid rule that the moderate Imami branch of Shi‘ism, the common heritage of the Twelver (Ithna‘ashari) and Ismaili Shi‘is, acquired its prominence during the imamate of Ja‘far al-Sadiq, while yet another politically active Shi‘i tradition found expression in Zaydi Shi‘ism.