Jacobus Willem Francois Pretorius, commonly known as Kosie Pretorius (born 5 September 1935), is a Namibian politician. He is the Chairman of the Monitor Action Group party, which mainly represents conservative white Namibians, and was a member of the National Assembly of Namibia from 1990 to 2005.
Pretorius was born in Swakopmund, Erongo Region. He earned his B.A. and M.A. from what was then the University of the Orange Free State in Bloemfontein, South Africa now known as the University of the Free State in 1956 and 1959, respectively. While there, he was an organising secretary of the Afrikaner Student Union.
Pretorius was a member of the all-white Legislative Assembly of South West Africa for Gobabis from 1962 to 1989. From 1981 until the founding of Action Christian National (ACN) party in 1989, Pretorius was the leader of the National Party in what was then South West Africa, an extension of the then ruling party of South Africa. He was also Minister of Water Affairs, and Post and Telecommunications in the Transitional Government of National Unity from 1988 to 1989. Immediately prior to independence, he was an ACN member of the Constituent Assembly, which was in place from November 1989 to March 1990.
Following independence in March 1990, Pretorius was a member of the National Assembly from 1990 to 2005. He initially represented the ACN in the National Assembly, but became the Chairman of a new party, MAG, in 1991. He was subsequently the only member of MAG in the National Assembly. Pretorius was the MAG candidate in the November 2004 presidential election, in which he received 1.15% of the national vote, finishing last out of seven candidates.