Ali ibn al-Husayn al-Sajjad, also known as Zayn al-Abidin was the great-grandson of the Islamic prophet Muhammad, and the fourth imam in Shia Islam, succeeding his father, Husayn ibn Ali, his uncle, Hasan ibn Ali, and his grandfather, Ali ibn Abi Talib.

In Shia Islam, the Imamah is a doctrine which asserts that certain individuals from the lineage of the Islamic prophet Muhammad are to be accepted as leaders and guides of the ummah after the death of Muhammad. Imamah further says that Imams possess divine knowledge and authority (Ismah) as well as being part of the Ahl al-Bayt, the family of Muhammad. These Imams have the role of providing commentary and interpretation of the Quran as well as guidance.