Twelvers are the followers of the 12 imams they consider to be the only rightful successors of the Prophet Muhammad, beginning with Ali ibn Ali Talib, Muhammad's cousin and son-in-law. Sunnis recognize Ali as the fourth caliph, but founding commonalities between Sunnis and Shiites end with him: Some Muslims had never recognized the first three as legitimate caliphs, thus forming the nucleus of Islam's protesting Shiites.
The seeming subversion never sat well with Sunnis, whose habit it became mercilessly and brutally to persecute Ali's followers and assassinating subsequent imams, most spectacularly among those the killing in battle of Hussayn, or Hussein, the third Imam (626-680), on the plains of Karbala. The killing is most famously commemorated in the annual rituals of Ashura.
The copious bloodletting gave Twelvers their two most prominent characteristics, like birthmarks on their creed: a cult of victimology, and a cult of martyrdom.
Twelvers never had an empire of their own until the Safavid dynasty was established in Iran in the 16th century and the Qajar dynasty in the late 18th century, when Twelvers reconciled the divine and the temporal in the leadership of the reigning imam. Ayatollah Ruhollah Khomeini, through his revolution in Iran in 1979, pushed the fusion of the temporal and the divine furthest, adding a layer of ideological expediency, under the banner of "Supreme Leader." "A strategic revolutionary," in the words of writer Colin Thubron, Khomeini "created his own Islamic state above Islamic law."