Husayn ibn Ali (626-680) was the younger son of Ali and Fatimah, and thus a grandson of the Prophet Muhammad, who is remembered to have cherished him deeply. In the reckoning of Twelver Shia Islam he is the third Imam, following his father Ali and his elder brother Hasan, and one of the Ahl al-Bayt, the People of the House.
His significance turns on a refusal. After the death of the Umayyad caliph Mu'awiya in 680, the caliphate passed to his son Yazid, whose legitimacy and conduct Husayn would not endorse. Pressed to give the oath of allegiance, Husayn declined, and in response to appeals from the people of Kufa in Iraq, who invited him to lead them, he set out from Mecca toward Iraq with his family and a small band of followers.
The promised support did not materialize. Kufa was brought under Umayyad control before he arrived, and Husayn found himself, with fewer than a hundred fighting men and their families, intercepted on the plain of Karbala by a large Umayyad force. What followed there became the central sacred drama of Shia Islam.