Cornelis Hermanus Antonius "Kees" Koster (13 July 1943 – 21 March 2013) was a Dutch computer scientist who was a professor in the Department of Informatics at the Radboud University Nijmegen in the Netherlands. Born in Haarlem, his family moved to Jakarta after the war. At the age of 11 he returned to the Netherlands on his own. After his study at the University of Amsterdam he worked at the Mathematisch Centrum (MC) in Amsterdam under Adriaan van Wijngaarden.