A spy was an individual who worked in espionage.
The Doctor and/or his companions were accused of being spies on many occasions, usually because of their lack of identification and appearing seemingly impossibly without anyone having record of them. Among those who made the accusations based on these factors included Eldred, (TV: The Time Meddler) Odysseus and Cassandra, (TV: The Myth Makers) General Smythe, Lt Lucke, (TV: The War Games) Brigade Leader Alastair Lethbridge-Stewart, (TV: Inferno) Ortron, (TV: The Monster of Peladon) Tuar, (TV: Planet of the Spiders) the Marshal of Atrios, (TV: The Armageddon Factor) Daisy K (TV: The Happiness Patrol) and Rutan spy Heinz Bruckner. (COMIC: The Instruments of War)Miles Barrington Smythe was a Russian spy in 1963 London. (TV: The Cambridge Spy)