Imam Husayn ibn Ali (Arabic: الحسين بن علي, romanized: al-Ḥusayn ibn ʿAlī; 11 January 626 – 10 October 680) was a social, 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,[9] Husayn is regarded as the third Imam (leader) in Shia Islam after his brother, Hasan, and before his son, Ali al-Sajjad. Being the grandson of the prophet, he is also a prominent 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.[10][11]

During the caliphate of Ali, Husayn accompanied him in wars. After the assassination of Ali, he obeyed his brother in recognizing the Hasan–Mu'awiya treaty, despite it being suggested to do otherwise. In the nine-year period between Hasan's abdication in AH 41 (660 CE) and his death in AH 49 or 50 (669 or 670 CE), Hasan and Husayn retreated to Medina, trying to keep aloof from political involvement for or against Mu'awiya.[12][13] After the death of Hasan, when Iraqis turned to Husayn, concerning an uprising, Husayn instructed them to wait as long as Mu'awiya was alive due to Hasan's peace treaty with him.[12] Prior to his death, Mu'awiya appointed his son Yazid as his successor, contrary to the Hasan–Mu'awiya treaty.[11] When Mu'awiya died in 680, Yazid demanded that Husayn pledge allegiance to him. Husayn refused to do so. As a consequence, he left Medina, his hometown, to take refuge in Mecca in AH 60 (679 CE).[11][14] There, the people of Kufa sent letters to him, invited him to Kufa and asked him to be their Imam and pledged their allegiance to him.[11] On Husayn's way to Kufa with a retinue of about 72 men, his caravan was intercepted by a 1,000-strong army of the caliph at some distance from Kufa. He was forced to head north and encamp in the plain of Karbala on 2 October, where a larger Umayyad army of some 4,000 or 30,000 arrived soon afterwards.[15] Negotiations failed after the Umayyad governor Ubayd Allah ibn Ziyad refused Husayn safe passage without submitting to his authority, a condition declined by Husayn. Battle ensued on 10 October during which Husayn was martyred along with most of his relatives and companions, while his surviving family members were taken prisoner. The battle was followed by the Second Fitna, during which the Iraqis organized two separate campaigns to avenge the martyrdom of Husayn; the first one by the Tawwabin and the other one by Mukhtar al-Thaqafi and his supporters.