His maternal uncle is English actor Malcolm McDowell, with whom he appeared in 2008 in Neil Marshall's Doomsday, and his paternal uncle is the former Sudanese Prime Minister Sadiq al-Mahdi. He is a great-great-great-grandson of Sudanese leader Muhammad Ahmad. He attended St Lawrence College, Ramsgate, Kent. Western culture required a surname, so El Fadil was taken from Sid's grandfather and was adopted as his surname when he moved back to England. He was credited under the shortened name Siddig El Fadil until October 1995. Three seasons into his run on Star Trek: Deep Space Nine, he changed his stage name to Alexander Siddig (stating he chose Alexander to honor his English heritage from his mother's side, and because he felt the name came without religious implications).