Shiism did not come into existence after Ali bin Abi Talib, but before Ali bin Abi Talib. To explain this fact is that we have a school called Shiism and we have a group of people called as Shia, this school emerged simultaneously with the Qur'an and the first person who supported this school and promoted this school and believed in this school was the beloved Prophet himself (Peace be upon him and his family), then Siddiqah Tahirah [Fatimah Al-Zahra] and Ali Ibn Abi Talib (peace be upon them) and other Ahl al-Bayt, then the people. Shia means a group that follows Ali Ibn Abi Talib (Peace be upon him), but Shiism means a school that believes in God's Wali (God's Guardian, Custodian, Saint, Caliph) and the successor of the Prophet to be infallible, and that infallible perfect human being is no one else except Ali and his children (peace be upon them). The first individual who believed in this school was the Prophet himself, because [the holy Qur'an says:]
﴿آمَنَ الرَّسُولُ بِما أُنْزِلَ إِلَیهِ مِنْ رَبِّهِ وَ الْمُؤْمِنُونَ﴾.[
The Messenger believed in what was revealed to him from his Lord, and the believers [also believed it]. [1]
The Shi'ite school is different from Shia and a special group. The first founder and believer of the Shi'ite school was the holy essence of the Holy Prophet and the Commander of the believers, peace be upon them. If the blessed Messenger of God believed in his own prophethood, his excellency, the Command of the believers also believed in his own guardianship [Wilayah]. Such is the school of Shia. So, if someone does not accept the Wilayah, and if someone does not consider the blessed Commander of the believers (peace be upon him) as the immediate caliph, such a person has believed in nothing!
[1]. Surah Baqarah, verse 285
#Grand_Ayatollah_Javadi_Amoli
Books: Speech at Ghadir International Congress
Date: 11/08/2013