Spies have made an extraordinary impact on the history of the 20th Century, but fourteen in particular can be said to have been demonstrably important. As one might expect, few are household names, and it is only with the benefit of recently declassified files that we can now fully appreciate the nature of their contribution.The criteria for selection have been the degree to which each can now be seen to have had a very definite influence on a specific course of events, either directly, by passing vital classified material, or indirectly, by organizing or managing a group of spies. Those selected were active in the First World War, the inter-war period, the Second World War, the Cold War and even the post-Cold War era.These include Walther Dewé who formed a spy ring in German-occupied Belgium during the First World War. This train-watching network, known as ‘White Lady’, reported on German troop deployments and possible weaknesses in the German...Spies have made an extraordinary impact on the history of the 20th Century, but fourteen in particular can be said to have been demonstrably important. As one might expect, few are household names, and it is only with the benefit of recently declassified files that we can now fully appreciate the nature of their contribution.The criteria for selection have been the degree to which each can now be seen to have had a very definite influence on a specific course of events, either directly, by passing vital classified material, or indirectly, by organizing or managing a group of spies. Those selected were active in the First World War, the inter-war period, the Second World War, the Cold War and even the post-Cold War era.These include Walther Dewé who formed a spy ring in German-occupied Belgium during the First World War. This train-watching network, known as 'White Lady', reported on German troop deployments and possible weaknesses in the German defences. Extending its operations into northern France, the ring provided 75 pe