William John Christopher Vassall (20 September 1924 – 18 November 1996) was a British civil servant who spied for the Soviet Union under pressure of blackmail. Although operating only at a junior level, he was able to provide details of naval technology which were crucial to the modernising of the Soviet Navy. He was sentenced to eighteen years' jail, and was released after ten. The Vassall scandal greatly embarrassed the Macmillan government, but was soon eclipsed by the more dramatic Profumo affair.
John Vassall (as he was always known) was born in 1924, the son of William Vassall, chaplain at St Bartholomew's Hospital, London, and Mabel Andrea Sellicks, a nurse in the same hospital. He was educated at Monmouth School. In World War II, he worked as a photographer for the Royal Air Force. After the war, in 1948, he became a clerk at the Admiralty.
Although his father was an Anglican priest, his mother converted to Roman Catholicism (a fact which led to some tensions in their marriage), and John himself converted in 1953.
In 1952, Vassall was appointed to the staff of the Naval Attaché at the British embassy in Moscow. There he found himself socially isolated by the snobberies and class hierarchies of diplomatic life, his loneliness further exacerbated by his homosexuality (a practice that was illegal in both Britain and the Soviet Union at the time). He became acquainted with a Pole named Mikhailsky, who worked for the Embassy, and who introduced him to the homosexual underworld of Moscow. In 1954, he was invited to a party, where he was encouraged to become extremely drunk, and where he was photographed in compromising positions with several men.