Sadiq al-Mahdi, also known as Sadiq as-Siddiq, was a Sudanese political and religious figure who was Prime Minister of Sudan from 1966 to 1967 and again from 1986 to 1989. He was head of the National Umma Party and Imam of the Ansar, a sufi order that pledges allegiance to Muhammad Ahmad (1844-1885), who claimed to be the Mahdi, the messianic saviour of Islam.