Shāh Karim al-Husayni (Arabic: شاه كريم الحسيني, romanized: Shāh Karīm al-Ḥusaynī; born 13 December 1936), known by the religious title Mawlānā Hazar Imam by his Ismaili followers and elsewhere as Aga Khan IV, is the 49th and current Imam of Nizari Ismailis. He has held the position of imam and the title of Aga Khan since 11 July 1957, when, at the age of 20, he succeeded his grandfather, Sir Sultan Muhammad Shah Aga Khan III. The Aga Khan claims direct lineal descent from the Islamic prophet Muhammad through Muhammad's cousin and son-in-law, Ali, considered an imam in Shia, and Ali's wife Fatima, Muhammad's daughter from his first marriage.

His grandfather, Aga Khan III, states in his memoirs that the Shias had a "need (for) Divine guidance" after the Prophet of Islam's death, this need being fulfilled by the Imamate. According to the Aga Khan III as mentioned in his memoirs, he has actual "Divine power, guidance, and leadership (authority)." The Institution of Imamate has continued to present day with the Aga Khan IV as the 49th Imam of the Ismaili Community. The Aga Khan is a business magnate with British and Portuguese citizenship, as well as a racehorse owner and breeder.

Aga Khan's net worth has been estimated at $13.3 billion. Forbes describes the Aga Khan as one of the world's fifteen richest royals. He is the founder and chairman of the Aga Khan Development Network, one of the largest private development networks in the world.

Since his ascension to the Imamate of the Nizari Ismailis in 1957, the Aga Khan has been involved in complex political and economic changes which have affected his followers, including the independence of African countries from colonial rule, the expulsion of Asians from Uganda, the independence of Central Asian countries such as Tajikistan from the former Soviet Union and the continuous turmoil in Afghanistan and Pakistan. Aga Khan IV became the first faith leader to address the Joint Session of the Parliament of Canada on 27 February 2014.