Jan Willem (or Wilhelm) Ter Braak (originally Engelbertus Fukken) (c. 1914 – c. 29 March 1941) was a Dutch espionage agent working for Germany who operated for five months in the United Kingdom. Although his active period was short, Ter Braak is believed to have been the German agent who was at large for the longest time in Britain during the Second World War. When he ran out of money, Ter Braak committed suicide in a public air raid shelter.