Shah Karim Al-Hussayni, also known simply as the Aga Khan (Imamate: 1957-present), is the leader of the Shia sect of Muslims known as the Nizari Ismailis. For 10–15 million Nizari Ismaili Muslims the Aga Khan is the 49th hereditary Imam, with lineage descending back to Ali, the cousin of the Prophet Muhammad (PBUH).