Aga Khan (Persian: آغا خان‎; also transliterated as Aqa Khan and Agha Khan) is the hereditary title of the Imam of the largest branch of the Ismā'īlī followers of the Shī‘a faith. They affirm the Imamat of the descendants of Ismail ibn Jafar, eldest son of Imam Ja'far al-Sadiq, while the larger Twelver branch of Shi`ism follows Ismail's younger brother Musa al-Kazim and his descendants.

Abdullah Jafar bin Muhammad As-Sadiq's sons, Ismail bin Jaffar and Abul Hassan Musa bin Jaffar, are followed by Twelver Shiites.^{[citation needed]}A third son, Ismail bin Jafar, died during childhood.

The Fatimid kingdom was ruled by seven successors, after which a dispute developed between two princes – Nizar and Mustali – which resulted in the defeat of the Nizaris, many of whom left Egypt for the region of Iran.

In the 1st half of the 19th century when the Nizārī Imams still lived in Iran the honorific title of "Aga Khan" was bestowed upon Aga Hasan Ali Shah, the 46th Imam of the Ismailis, by Fat′h-Ali Shah Qajar, the Shah of Persia. Etymologically the title combines the Turkish military title Agha, meaning a "noble" or "lord", with the Turko-Mongol title Khan for a local ruler, so the combination means roughly "Commanding Chief". In Persia's Qajar court protocol, Khan (and Amir) was commonly part of commanders of armed forces and provincial tribal leaders which ranked fourth in precedence amongst the eight title classes for non-members of the dynasty...

The abbreviation AGA and the word Aga may refer to:

Khan may refer to: