Brother some school of thoughts were found years after the death of Prophets… Where as the first Imam of Shia sect Hazrat Ali A.S was there during the time of Prophet P.B.U.H. There are a number of hadith’s of Prophet which mentions about his pious personality and his status in the eyes of Prophet and Allah SWT. He and his descents had served a great source of knowledge and served there lifes in the way of Islam. Also as the brother mentioned some of the Imams of the other school of thoughts were students of Imam Jaffar Said who happens to be the sixth Imam.
Following website is quite informative about this sect:
To learn more about the Imammat of Hazrat Ali A.S. Please refer to the following website:
Ghadir Khumm: In Qur’an, Hadith and History
Also, to learn about the knowledge and personality of Hazrat Ali. Please read the following book which is a compilation of his sermons and letter
Nahjul Balagha (Peak of Eloquence)
Jazakallah