Aga Khan is a title of the spiritual leader, Imam, of the Nizari sect within the Ismaili branch of Islam (Nizari Ismaili). The first Imam to bear the title of Aga Khan was Aga Hasan Ali Shah in the mid 19th century. The title Aga Khan means "Great Chief" and was bestowed upon Imam Aga Hasan Ali Shah by the Shah of Persia. The ditary Imam of the Shia Imami Ismaili Muslims is the direct descendant of Muhammad through his cousin and son-in-law, Ali, the first Imam, and his wife Fatima, Muhammad's daughter.List of those who have held the title of Aga Khan
Aga Khan I = Aga Hasan Ali Shah = HH Shah Hasan Ali Shah Mehalatee Aga Khan I (1800-1881), 46th Imam (1817-1881)
Aga Khan II = HH Ali Shah Aga Khan II (about 1830 - 1885), 47th Imam (1881-1885)
Aga Khan III = HRH Prince Sultan Mohammed, (1877-1957), 48th Imam (1885-1957)
Aga Khan IV = Karim Aga Khan = HH Prince Aga Khan IV = Prince Karim El Husseni (b. 1936), 49th Imam of the Ismailis (from 1957)
Aga Khan IV, CC, BA (Prince Karim Aga Khan or Prince Karim El Husseni) (born December 13, 1936) is the current (49th) Imam of the Shia Imami Ismaili Muslims since July 11, 1957. He is referred to by members of his community as Hazar Imam, or "Present Imam".At the age of 20 he succeeded his grandfather, Sultan Mahommed Shah, as Imam. He is the 49th direct descendant of the Prophet Muhammad through the Prophet's daughter, Fatima, and her husband, Ali, the first Shia Imam. Aga Khan IV is the son of Prince Ali Solomon Khan, (November 17, 1911 - May 12, 1960), and his first wife, Hon. Joan Yarde-Buller, daughter of the 3rd Baron Churston, renamed Princess Tadjudowlah, (b. 1908). He was born in Geneva. He spent his early childhood in Nairobi, Kenya, and then attended the Institut Le Rosey in Switzerland. He graduated from Harvard University in 1959 with a BA Honors Degree in Islamic history. Early education included private tutoring, with Prince Sadruddin, by Mustafa Kamil, a scholar from Aligarh Muslim University engaged by his grandfather, Aga Khan III. He married his first wife, former model Sarah Frances (Sally) Crocker-Poole, titled HH Begum Salima, on 22 October 1969. The marriage, which ended in divorce after 25 years, produced three children. Aga Khan IV has British nationality. He married his second wife, Dr. Gabriele zu Leiningen (born in Frankfurt-am-Main on 1 April 1963), in Aiglemont on 30 May 1998. From then on, his wife took on the name Begu Inaara. On 8 October 2004, an announcement was made that the Aga Khan and she were to seek a divorce. They have one son. Founded and guided by the Aga Khan, the Aga Khan Development Network (AKDN) brings together a number of development agencies, institutions, and programmes that work primarily in the poorest parts of Asia and Africa. AKDN is a contemporary endeavour of the Ismaili Imamat to realise the social conscience of Islam through institutional action. AKDN agencies conduct their programmes without regard to the faith, origin or gender. The Aga Khan is reported to be among the wealthiest people in the world. Among other interests, he is known for his equestrian pursuits and for success in race horse breeding particularly after acquiring the bulk of the breeding stock from the estate of Marcel Boussac in 1980. He was made an Honorary Companion of the Order of Canada in 2005. He built the Aga Khan University and Hospital in Karachi, Pakistan, in 1983. Also, Aga Khan schools are widely known in third world countries such as Uganda, Kenya, and Tanzania.