Guy Francis de Moncy Burgess was a British diplomat and Soviet double agent, and a member of the Cambridge Five spy ring that operated from the mid-1930s to the early years of the Cold War era. His defection in 1951 to the Soviet Union, with his fellow spy Donald Maclean, led to a serious breach in Anglo-United States intelligence co-operation, and caused long-lasting disruption and demoralisation in Britain's foreign and diplomatic services.

The Cambridge Five was a ring of spies in the United Kingdom that passed information to the Soviet Union during the Second World War and the Cold War and was active from the 1930s until at least the early 1950s. None of the known members was ever prosecuted for spying. The number and membership of the ring emerged slowly, from the 1950s onwards.