The Khawarij or Kharijites ("seceders") were the first sect to split away from mainstream Islam. Some consider them a branch of the Shia.The same Arabic root (kh-ra-ja) from which comes their name also means "to throw out," and denotes their revolutionary commitment to ridding Islam of the apostate elements of their day, namely the Umayyads. While they did not fully emerge until after the death by murder of the third caliph, Uthman (644-656), it is clear from early Kharijite sermons that their movement began to crystallize during the rule of Uthman whom they accused of introducing "innovation" into Islam.
In their view, Mu'awiyya and his Umayyad followers had to be driven out because they failed to properly avenge Uthman's murder. Furthermore, the Kharijites challenged the legitimacy of the next caliph, Ali (656-661), because, following an inconclusive military encounter with the Umayyads at the Battle of Siffin (658), Ali had agreed to submit the dispute over the caliphate to a process of binding arbitration, which was decided in favor of the Umayyads. These events rendered both the Umayyads and Ali infidels in the eyes of the Kharijites. The Kharijites assassinated Ali at his capital Kufa in 661. He was buried in the nearby city of Najaf, a major Shia shrine.
The Kharijites were rigorous puritans and fundamentalists who combined radical egalitarianism (even a slave could become caliph in their view) with revolutionary zeal. Their example inspired the 11th c. al-Moravids and 12th c. al-Mohads in North Africa and such modern extreme Islamist groups Takfir wa-l Hijra and Islamic Jihad. In style and tone, they were like the 18th c. Wahhabis.