The Shi‘i Ismaili Muslims, better known today as the Ismailis, make up the second largest branch of Shi‘i Islam after the Twelvers (Ithna ‘Ashariyyah). Shi‘i Muslims believe that the Prophet Muhammad’s divinely-ordained spiritual authority and divinely-inspired knowledge continues in members of his family, beginning with his cousin and son-in-law ‘Ali b. Abi Talib, and a specific lineage of his descendants. This office of religious authority and leadership is called the Imamat (Imamah) and forms the core doctrinal principle of the major branches of the Shi‘a – the Twelvers (Ithna Asharis), the Ismailis, and the Zaydis.
The Ismailis trace the Imamat through a particular lineage of Imams descended from Isma‘il (d. after 755), the son of Ja‘far al-Sadiq (d. 765); meanwhile, the Twelvers trace the Imamat through Musa, a younger son of Ja‘far al-Sadiq (see Figure 1). The Ismailis later divided over the question of the successor to the eighteenth hereditary Imam al-Mustansir (d. 1094).
One group, the Tayyibi Ismailis, followed the Imamat of the Imam Mustansir’s younger son al-Musta‘li and his descendants. Today the Tayyibis are called Bohras and are divided into three major branches – the Da’udi Bohras, the Sulaymani Bohras, and the Alavi Bohras – each of whom recognizes a different da‘i al-mutlaq (absolute missionary) as the chief representative of the Tayyibi Ismaili Imamat, whose lineage is believed to have gone into concealment with its twenty-first Imam al-Tayyib in 1230. The Da’udi Bohras led by Syedna Mufaddal Saifuddin (b. 1946) make up the largest Bohra community today.
Another group, the Nizari Ismailis, recognized the Imamat of al-Mustansir’s elder son and heir-designate Nizar and traced the Imamat in his progeny; The Nizari Ismailis are the only Shi‘a Muslim community led by a visible hereditary Imam, Mawlana Shah Karim al-Husayni Aga Khan IV (b. 1936), the forty-ninth Imam. Today, the term “Ismailis” is most often used to refer to the Nizari Ismailis.