The Original Mission: Impossible

Steven Hill as Dan Briggs and Martin Landau as Rollin Hand (in disguise) in the premiere episode, September 17, 1966.

Mission: Impossible is an American television series that was created and initially produced by Bruce Geller. It chronicles the missions of a team of secret government agents known as the Impossible Missions Force (IMF). In the first season, the team is led by Dan Briggs, played by Steven Hill; Jim Phelps, played by Peter Graves, takes charge for the remaining seasons. A hallmark of the series shows Briggs or Phelps receiving his instructions on a recording that then self-destructs, followed by the theme music composed by Lalo Schifrin.

The series aired on the CBS network from September 1966 to March 1973, then returned to television for two seasons on ABC, from 1988 to 1990, retaining only Graves in the cast. It later inspired a popular series of theatrical motion pictures starring Tom Cruise, beginning in 1996.

This section does not cite any references or sources. (December 2011)
The series follows the exploits of the Impossible Missions Force (IMF), a small team of secret agents used for covert missions against dictators, evil organizations and (primarily in later episodes) crime lords. On occasion, the IMF also mounts unsanctioned, private missions on behalf of its members.
The identities of the organization that oversees the IMF and the government it works for are never revealed. Only rare cryptic bits of information are ever provided during the life of the series, such as in the third season mission "Nicole", where the IMF leader states that his instructions come from "Division Seven". In the 1980s revival, it is suggested the IMF is an independent agency (as the FBI can only legally operate within the United States and the CIA can only operate outside the country). In the first motion picture, unlike the TV show, the IMF is depicted as part of the CIA.
http://en.wikipedia.org/wiki/Mission:_Impossible