This is the Mausoleum of Mohammed Shah Aga Khan. He was the spiritual leader of the Ismailis, a Shiite Sect, with followers around the world (mainly in India).
The Aga Khan succeeded his father in 1885, and was succeeded by his son upon his death in 1957. If you come to Aswan you can visit his white Carrara marble tomb, where his widow placed a red rose every day.