During her first season, Diana Rigg was dismayed to find out that the cameraman was being paid more than she was. She demanded a raise, to put her more on a par with her co-star, or she would leave the show. The producers gave in, thanks to the show's great popularity in the U.S.
Diana Rigg was the first person ever to do Kung Fu on-screen. In 1965, Ray Austin went to his producers and said, "Listen, I want to do this thing called Kung Fu." They said "Kung what?" and insisted that Emma, like her predecessor, stick to judo. Instead, Austin secretly taught Rigg Kung Fu.
The look and character of Steed is an amalgam of Patrick Macnee's father (a racehorse trainer and dandy), fictional character The Scarlet Pimpernel, and Macnee's commanding officer in the Navy.
Series writer Brian Clemens noted in an interview the sexual chemistry that particularly existed between Steed and Emma Peel, and the common question of "Will they ever go to bed together?" Clemens' attitude toward the characters was that they already had done, and this was the next day. Patrick Macnee and Dame Diana Rigg confirmed later in interviews that they had decided their characters had a casual sexual relationship, "but just didn't dwell on it."
Emma Peel's name was taken from the British movie industry expression "M-Appeal", or "man-appeal", which is what the show's producers were looking for in her character.