Balthazar Johannes "B. J." Vorster was a South African apartheid politician who served as the prime minister of South Africa from 1966 to 1978 and the fourth state president of South Africa from 1978 to 1979. Known as B. J. Vorster during much of his career, he came to prefer the anglicized name John in the 1970s.

The prime minister of South Africa was the head of government in South Africa between 1910 and 1984.