Captain Sigismund Payne Best OBE was a British Secret Intelligence Service agent during the First and Second World Wars. He was captured by German Gestapo and Sicherheitsdienst (SD) men on 9 November 1939 in the Venlo Incident.

The Secret Intelligence Service (SIS), commonly known as MI6, is the foreign intelligence service of the United Kingdom, tasked mainly with the covert overseas collection and analysis of human intelligence on foreign nationals in support of its Five Eyes partners. SIS is one of the British intelligence agencies and the Chief of the Secret Intelligence Service ("C") is directly accountable to the Foreign Secretary.