The earliest Muslim sect. They were alienated by Ali's acceptance of arbitration with Mu'awiyah in 659 CE after the death of Uthman, the third Caliph; murdered Ali, the fourth Caliph; and remained a thorn in the side of the caliphate until the Abbasid period.
Their rigourous puritanism later inspired the al-Moravids and al-Mohads in north Africa, and also influence modern Islamist groups.
They survive today as the Ibadhi group in Oman and the Maghreb.
This is NOT the place for theological discussions.