Simeon Olaosebikan Adebo (1914-1994) was appointed United Nations Deputy Secretary General and Director General of UNITAR in 1969, and stayed with the Institute until 1972. Born in Western Nigeria, he became an Okanlomo (Chief) of the Yoruba people. After obtaining a degree in law from London University and being admitted to the bar, he continued his career at the Nigerian Ministry of Finance and the Treasury and in 1961 became head of the Civil Service and Chief Secretary to the Government of Western Nigeria.

In 1962, Chief Adebo moved to New York to represent his country at the United Nations. After having served as Ambassador, he took up, in 1969, an appointment with UNITAR. As head and member of a number of associations, he was actively engaged in a variety of activities targeting the promotion of democratic values and the enhancement of the effectiveness of development policies. Upon return to his home country, he headed several corporations as well as the National Universities Commission and the National Institute for Policy and Strategic Studies. He had also served as chancellor, first, of Obafemi Awolowo University and, later for eight years, of Lagos University.