The Professionals is a British crime-action television drama series produced by Avengers Mark1 Productions for London Weekend Television (LWT) that aired on the ITV network from 1977 to 1983. It starred Martin Shaw, Lewis Collins and Gordon Jackson as agents of the fictional "CI5" (Criminal Intelligence 5, alluding to the real-life MI5).

CI5 (Criminal Intelligence 5) is a British law enforcement department, instructed by the Home Secretary to use any means to deal with crimes of a serious nature that go beyond the capacity of the police, but which are not tasks for the Security Service or the military.

More Info: en.wikipedia.org