Grandson of Muhammad's son Husayn, son of Ali Zayn al-Abidin. Shii sect of Zaydis believed he was the fifth imam. He rejected the notion of the Hidden Imam, pursuing instead a more activist revolutionary position against the Umayyad dynasty. Led a rebellion against them in 740. First descendant of Husayn to rebel openly against the Umayyads. His leadership resulted in his followers declaring that any descendant of Fatimah and Ali could claim the imamate; the determining factor was not birth order but a public assertion of the imamate. He died violently in rebellion. Today he serves as a symbol for Shiis, encouraging activism, rather than passive acceptance, in response to suffering, injustice, and oppression.