The Union of South Africa was promulgated on 31 May 1910 after negotiations, which excluded black South Africans. The Union entailed the amalgamation of the four colonies in southern Africa (Orange Free State, Tranvaal, Natal and the Cape Colony) into a single political entity, which was itself a self-governing Dominion in the British Empire. The government of the Union was therefore subject to the Head of State of the British Empire, i.e. the King of England (at that time) who was represented in South Africa by an appointed Governor-General to whom the Prime Minister of the Union (the elected Head of Government of the Union) accounted. The Governor-General also represented the government of Britain as High Commissioner, i.e. (In these twin positions, his responsibilities also extended to the then Basutoland (now Lesotho), Bechuanaland (Botswana) and Swaziland.
State Presidents of the Republic
Following a racially-based referendum which excluded black people, South Africa was declared a Republic on 31 May 1961 and under international pressure withdrew from the Commonwealth of Nations (which had replaced the British Empire). With the onset of the Republic, the Office of the Governor-General was abolished and the position of State President was created as the figurative head of state (a situation which remained from until 1983 when under the Tricameral Parliament, the position became substantive and effectively displaced the significance of the Prime Minister. The position of Prime Minister was eventually abolished in 1984).
The position of a Prime Minister was established in 1910, with the formation of the Union of South Africa. This position was the highest elected political office in the Union. It was abolished in 1984 by State President Willem De Klerk, when, under the Tricameral Parliament (established in 1983) the political significance of the position of the State President was increased and the position of Prime Minister became more and more superfluous.
Presidents of the Republic
Prior to the first non-racial elections in April 1994, South Africa adopted an interim constitution which provided for the position of President. The 1994 interim constitution finally gave way to the final constitution in 1996 which retained the position of President.