Immediately after the death of Muhammad, 'Islam' was divided into two major sects. The most prominent were the Sunnis (Orthodox). The second were the Shiites (the Party of Ali).
Sunnis are also referred to as Ahlu^Sunnah (people who follow the example of Muhammad). The word Sunni is derived from the word Sunna which means the words and deeds or example of Muhammad.
Sunnis believe in an elected Caliphate as the logical sequence in the footsteps of Muhammad. They represent the branch of Islam that accepted the caliphate of Abu Bakr due to him being chosen by a majority, through a process of Consultations, or Shurah.
The caliphate is the first distinguishing factor of Sunni Islam.
Sunni 'Islam' is a theological grouping which theoretically derives its power through the consent of the community in contradistiction from the Shi'ites whose religious elite are unrepresentative and authoritarian.
Sunnis are divided into four rites - orthodox schools of Sunni law - called Madhahib or schools of Islamic Law and practice:
Hanbali, Hanafi, Shafi'I and Maliki.
Among the Shafi'I school are the six accepted compilers of the Ahadith:
Bukhari, Muslim, Tirmidi, Majah, Abu Dawud and Nasi.
These collections are considered second to the Quran in importance. It is relevant to point out that in Sunni tradition, the Mahdi is Jesus who will return to earth as a 'Muslim' to slay the anti-Christ called al Dajjal.
Muhammad himself mentioned and described this apocalypltic encounter in the Ahadith as in Muslim Hadith 7023. The Wahabis of Arabia of today are the standard bearers of this sect of 'Islam'.
Sunni Muslims are by far the largest - over 85% - denomination of Islam.