The first Caliph Abu Bakr Assedik
The main variance between the shia and the sunni occurred after the death of the holy prophet .the shia believes that the prophet is ordered by Allah to express Ali Ibn Abitali as his succeSsor in Gadir- Ghom and according TO lots other evidences.but after the death of the prophet ,some of his companion did not obey the prophet speech and chose Abu-baker as the prophet successor.
Hi a simple answer Shiites say: Prophet Muhammad has chosen Ali as his successor, but Sunnis say that has not happened.
the disputes between these two sects mainly cuased from different views about authority particularly who is the successor of the prophet and also from teaching of islam religion.
the successor of prophet mohammed peace be upon him is hazrat syedina abu bakar siddique r.a
the death of holy prophet Muhammad peace be upon him led to split between shia and Sunni. of course according to Shiite, the holy prophet before his death in different places and position like "the pool" or Qadir Khom announced that Imam Ali is one who selected as his right successor.
Abou Bakr Assidiq was elected by Muslims as prophet Muhammad (PBUH) successor of the prophet death.
Muhamad didn't name a successor and a schism between Sunni and Shia born. The Shia claimed the right of Ali, the son-in-law of the Prophet Muhammad, and his descendants to lead the Islamic community. Sunnis assert that even though Muhammad never appointed a successor, Abu Bakr was elected first caliph by the Muslim community.
Prophet Muhammad.
Acoording the Quran and speeches of prophet, Shia Muslims believe that just as a prophet is appointed by God alone, only God has the prerogative to appoint the successor to his prophet. They believe God chose Ali to be Muhammad's successor, infallible, the first caliph (khalifa, head of state) of Islam. Muhammad, before his death, designated Ali as his successor. Ali was Muhammad's first cousin and closest living male relative as well as his son-in-law, having married Muhammad's daughter Fatimah.
Acoording the Quran and speeches of prophet, Shia Muslims believe that just as a prophet is appointed by God alone, only God has the prerogative to appoint the successor to his prophet. They believe God chose Ali to be Muhammad's successor, infallible, the first caliph (khalifa, head of state) of Islam. Muhammad, before his death, designated Ali as his successor. Ali was Muhammad's first cousin and closest living male relative as well as his son-in-law, having married Muhammad's daughter Fatimah.
sunni
The death of the Prophet Muhammad. It was then decided that as a religious and community leader he should be succeeded, and such a religious successor was called a Caliph; the region and community he ruled over, a Caliphate. This immediately led to the first schism, namely between Shi'ite and Sunni Muslims. The Sunni Muslims considered Muhammad's father-in-law the rightful successor and first Caliph, the Shia Muslims considered his son-in-law the rightful successor.