Emma Peel, memorably played by Diana Rigg, made her debut on the show in 1965 -- the same year it started to air in the U.S. after a few years already airing on British television.
Before Emma, the sidekick (and she did kick) to suave secret agent John Steed (Patrick Macnee) was Dr. Cathy Gale (played by Honor Blackman, later of "Goldfinger").
But the Emma Peel era tends to be the favorite of many "Avengers" fans. She was sexy, tough, smart, independent and funny. Plus, those catsuits.
The Emma Peel episodes have recently re-appeared on a revamped, reasonably priced DVD set after being out of print, and available only at high prices, for several years.
I also recently came across a batch of lesser-seen pics from that era of the show. Here's a look: