Isma'il ibn Ja'far (Arabic: إسْماعِيل ٱبْن جَعْفَر ٱلْمُبَارَك, romanized: Ismāʿīl ibn Jaʿfar al-Mubārak) was the eldest son of Ja'far al-Sadiq and the sixth Imam in Isma'ilism. He carried the epithet of al-Mubarak, on the basis of which one of the earliest Isma'ili groups became designated as the Mubarakiyya.
It seems likely that the Mubarakiyya were originally supporters of Isma'il before acknowledging Muhammad ibn Isma'il as their Imam. At any rate, Mubarakiyya was thus one of the original names of the nascent Isma'iliyya, a term coined by later heresiographers. A faction of the Mubarakiyya later developed into the Fatimid Isma'ilis, upholding the continuity of the Imamate in the progeny of al-Mubarak, acknowledging al-Mubarak himself as their sixth Imam. This enumeration was subsequently retained by the various branches of the Isma'ili.
