The Ismailis are a branch of Shia Muslims who share a common history with the mainstream Shias, also known as “Twelvers” or “Ithnasheris”. A dispute, however, arose on the succession of the Sixth Imam, Ja'far al-Sadiq. The Ismailis accepted Imam Jafar al-Sadiq’s eldest son “Ismail” as a rightful seventh Imam. Mainstream Shias (Twelvers/Ithnasheris), on the other hand, accepted Imam Jafar al-Sadiq’s younger son "Musa al-Kazim" as their rightful Imam.