mole

In espionage jargon, a mole (also called a "penetration agent", "deep cover agent", "illegal" or "sleeper agent") is a long-term spy (espionage agent) who is recruited before having access to secret intelligence, subsequently managing to get into the target organization. However, it is popularly used to mean any long-term clandestine spy or informant within an organization (government or private). In police work, a mole is an undercover law-enforcement agent who joins an organization in order to collect incriminating evidence about its operations and to eventually charge its members. The term was introduced to the public by British spy novelist John le Carré in his 1974 novel Tinker Tailor Soldier Spy and has since entered general usage, but its origin is unclear, as well as to what exten...