Husayn ibn Ali was an Alid political and religious leader. The grandson of the Islamic prophet Muhammad and a son of Ali ibn Abi Talib and Muhammad's daughter Fatima, as well as a younger brother of Hasan ibn Ali, Husayn is regarded as the third Imam in Shia Islam after his brother, Hasan, and before his son, Ali al-Sajjad. Being the grandson of the prophet, he is the member of the ahl al-bayt. He is also considered to be a member of the Ahl al-Kisa, and a participant in the event of the mubahala. Muhammad described him and his brother, Hasan, as the leaders of the youth of Paradise.

The Alids are those who claim descent from Ali ibn Abi Talib, the fourth Rashidun caliph and the first imam in Shia Islam. Ali was also the cousin and son-in-law of the Islamic prophet Muhammad. The main branches are the Hasanids and Husaynids, named after Hasan and Husayn, the eldest sons of Ali from his marriage to Fatima, the daughter of Muhammad. As the progeny of Muhammad, they are revered by all Muslims. The Alids have led various movements in Islam, and a line of twelve Alids are the imams in Twelver Shia, the largest Shia branch.