Daniel Charl Stephanus (Daantjie) Oosthuizen (1926-1969) was a philosopher and opposer of Apartheid. He received his initial philosophical training at the University of Stellenbosch, where he obtained a BA with distinction in 1945 and an MA cum laude in 1949. From 1947 he also studied at the Dutch Reformed Church Seminary in Stellenbosch, passing his examination in theology in 1949. He undertook further theological studies at the Free University in Amsterdam and later carried out research in philosophy at the University of Amsterdam. The subject of his doctoral thesis was the phenomenology of Edmund Husserl.

Soon after his MA graduation Oosthuizen became a junior lecturer in philosophy at the University of Stellenbosch. From 1955 to 1957, he lectured on the history of philosophy, logic, and ethics at the University of the Orange Free State in Bloemfontein. From January 1958 until his death in April 1969, he was Professor of Philosophy at Rhodes University in Grahamstown. He spent his sabbatical years at the University of Oxford with Gilbert Ryle as his tutor in 1962, and again in 1968. Although he was appointed Professor of Philosophy at the University of Utrecht in November 1968, he died before he was able to take up the post.

Oosthuizen did not publish widely; he utilised lectures, seminars, and public addresses to present his philosophical, theological, and political thinking. He specialised in epistemology and the philosophy of mind drawing on his early interest in existentialism and phenomenology. As a Christian he was deeply troubled by the political situation in contemporary South Africa and expressed his views on the subject through his actions and writings. He died suddenly in 1969 at the age of 43.