The origins of Kharijites lie in the strife over political supremacy over the Muslim community in the years following the death of Muhammad. The third Caliph, Uthman, was killed by mutineers in 656 AD, and a struggle for succession ensued between Ali, cousin and son-in-law of Muhammad, and Mu'awiya, governor of Damascus. The core of Ali's followers later became Shiites, but a group of tribes settled in Iraq who originally supported him rebelled in 658; they became known as Kharijites (in Arabic Khawārij, singular Khārijī, meaning 'those that seceded'). Ali defeated the military rebellion, but the Kharijites survived and an adherent of the movement murdered Ali in 661.
Kharijite theology was a form of radical fundamentalism, preaching uncompromising observance of the teachings of Quran in defiance of corrupt authorities. Extreme Kharijites considered moderate Muslims to be 'hypocrites' or 'unbelievers', who could be killed with impunity. Their communities expelled from their midst those who committed 'grave sins', defined as any action contrary to the Quran. Kharijites insisted that only the most pious members of the community should be entrusted with political power. Perhaps not surprisingly, the various Kharijite communities never agreed on who the most pious person was, and the movement remained politically fragmented throughout its existence.
With time the movement became more moderate and less antagonistic to mainstream Islam. The high point of the Kharijites' influence was in the years 690 to 730, when their main city, Basra, became a center of Islamic theology. Their insistence on the primacy of religion in political life was accepted into mainstream Islamic teaching and remains influential to this day.