The Avengers

The Avengers was a British mystery/science-fiction spy series that aired from 1961 to 1969. Patrick McNee starred as British secret agent John Steed throughout the series. There were several different actresses playing female agents alongside Steed, particularly Diana Riggs as Emma Peel (who was not the typical helpless girl sidekick).

Influences on Shadow Unit
Emma Bull listed The Avengers as one of the shows which Shadow Unit would "share DNA with" in the essay Sanding the Oyster: The Origins of Shadow Unit. (In fact, the picture associated with Emma's profile on the Shadow Unit message boards is an image of Emma Peel.

Links
IMDB page