Ismāʿīl ibn Ja‘far al-Mubārak (; c. Born:Shawwal 100 AH/719 AD) was the eldest son of Imam Ja'far al-Sadiq, and he was the full-brother of Abdullah al-Aftah. Their mother, Fatima bint al-Hussain'l-Athram bin al-Hasan bin Ali, was the first wife of Ja'far al-Sadiq. Following Ja'far's death, the Shia community split between the element that would become the Twelver Shia, and those who believed the Imamate passed through to Ismail's son; the Ismaili branch of Shia Islam is accordingly named for Ismail. According to both the Nizari and Mustaali Shia sects, he is the sixth Imam.