Aga Khan is a title held by the Imām of the Nizari Ismāʿīli Shias. Since 1957, the holder of the title has been the 49th Imām, Prince Shah Karim al-Husseini, Aga Khan IV. Aga Khan claims to be a direct descendant of Muhammad, the last prophet according to the religion of Islam.

The Nizaris are the largest segment of the Ismaili Muslims, who are the second-largest branch of Shia Islam after the Twelvers. Nizari teachings emphasize independent reasoning or ijtihad; pluralism—the acceptance of racial, ethnic, cultural and inter-religious differences; and social justice. Nizaris, along with Twelvers, adhere to the Jaʽfari school of jurisprudence. The Aga Khan, currently Aga Khan IV, is the spiritual leader and Imam of the Nizaris. The global seat of the Ismaili Imamate is in Lisbon, Portugal.