The term was introduced to the public by British spy novelist John le Carré in his 1974 novel Tinker Tailor Soldier Spy[3][4] and has since entered general usage, but its origin is unclear,[1] as well as to what extent it was used by intelligence services before it became popularized. Le Carré, a former British intelligence officer, said that the term "mole" was actually used by the Soviet intelligence agency, the KGB,[2] and that a corresponding term used by Western intelligence services was sleeper agent.[5] While the term mole had been applied to spies in the book Historie of the Reign of King Henry VII written in 1626 by Sir Francis Bacon,[1][2] Le Carré said he did not get the term from that source.