Ismail ibn Jafar was an important figure in early Islamic history, born in the 8th century. He was the son of Jafar al-Sadiq, a prominent Shia Imam, and is recognized as the founder of the Ismaili branch of Shia Islam. Ismail is known for his teachings and interpretations of Islamic law, which influenced many followers. After his father's death, Ismail's claim to leadership was contested, leading to a split among Shia Muslims. His followers believed he was the rightful Imam, while others accepted his brother, Musa al-Kadhim. This division laid the groundwork for the development of different Shia sects within Islam.