The show grew out of the 1960 series Police Surgeon starring Ian Hendry; when that series ended, ABC cast Hendry in a new show called The Avengers, which began as a story about him avenging his fiancée's murder alongside John Steed.
The role of nurse/receptionist Carol Wilson was originally offered to actress Jan Watson, who turned it down for a film role, and it went to Ingrid Hafner instead.
After Ian Hendry left to pursue a film career, Patrick Macnee was promoted to lead, and early scripts originally written for Hendry's Dr. Keel character were simply reassigned to Honor Blackman's Cathy Gale, which scriptwriter Dennis Spooner said is why she was put in leather outfits - it was cheaper than rewriting the dialogue.
An early theatrical film version was planned in late 1963 pairing Steed and Gale with American agents to appeal to the US market, but the project stalled when Honor Blackman was cast opposite Sean Connery in Goldfinger and had to leave the series.
Emma Peel's name came from writers wanting a character with 'man appeal'; an early working name was 'Samantha Peel', shortened awkwardly to 'Mantha Peel', before settling on the verbal shorthand 'M. Appeal' which became 'Emma Peel'.
Elizabeth Shepherd was originally cast as Emma Peel and filmed one and a half episodes before being let go for not being interesting enough on screen; Diana Rigg was cast after more than 80 actresses were auditioned in total, following a suggestion from casting director Dodo Watts.
Diana Rigg discovered during her first series that she was being paid less than the cameraman and threatened to quit unless given a raise on par with Patrick Macnee; producers relented due to the show's popularity in the US.
Diana Rigg disliked wearing leather and insisted on a new line of fabric athletic wear for the fifth series, leading to 'Emmapeeler' jumpsuits made of stretch crimplene fabric, later featured in a four-page TV Guide photo spread.
Producer John Bryce cast his then-girlfriend, 20-year-old newcomer Linda Thorson, as Tara King and had her hair bleached blonde, but the process damaged it so badly she had to wear wigs until her natural brown hair grew back.
Only three complete episodes from the first series survive today, preserved as 16mm film telerecordings, since videotapes of early episodes were routinely wiped and reused at the time; the missing episodes were later recreated as audio dramas by Big Finish Productions.
From the fourth series onward, production switched from 405-line videotape to 35mm film because British video was incompatible with the US NTSC format required for the newly signed American broadcast deal with ABC, which paid $2 million for the first 26 episodes.
Producer John Bryce was fired after a rough cut screening of his first three Tara King episodes went badly, forcing returning producers Brian Clemens and Albert Fennell to rewrite and reshoot material, including fixing a plot hole with the improvised line 'I came the pretty way.'
No farewell scene for Emma Peel had been filmed when Diana Rigg left the show, so she was recalled to shoot a tag scene for 'The Forget-Me-Knot' in which her on-screen husband was played by Steed's regular stunt double wearing a bowler hat and umbrella to resemble Steed from a distance.
Fight arranger Ray Austin introduced kung fu into the series during the fourth and fifth series, training with Chee Soo and incorporating Feng Shou kung fu and tai chi into fight scenes; Austin, Diana Rigg and Chee Soo were later awarded a Guinness World Record as the first people to demonstrate kung fu on British television.
The show's memorable theme by Laurie Johnson was based on a previously released instrumental called 'The Shake', capitalizing on the 1960s dance craze of the same name, and was rescored with a new trumpet counter-melody when Linda Thorson joined as Tara King.
Composer Laurie Johnson, busy scoring the film Hot Millions, had his keyboard player Howard Blake score several episodes of the final season in a style closely matching his own; these near-complete scores were released on a double-CD set in 2011 to mark the show's 50th anniversary.
American censors refused to air the episode 'A Touch of Brimstone', in which Emma Peel dons a corset and spiked collar as the 'Queen of Sin' and is whipped by a guest star; four other early Emma Peel episodes were also withheld from initial US broadcast due to content concerns.
Despite being popular in the UK and Europe, the Tara King era was scheduled by US network ABC opposite the number-one rated show in the country, Rowan and Martin's Laugh-In, contributing to the show's American cancellation and, subsequently, its end in Britain in 1969.
The steel-plated bowler hat and sword-hidden umbrella carried by Steed gave rise to the show's foreign-language titles, including the French 'Chapeau melon et bottes de cuir' ('Bowler hat and leather boots') and the German 'Mit Schirm, Charme und Melone' ('With Umbrella, Charm and Bowler Hat').
