The Prisoner was filmed in the North Wales resort village of Portmeirion over the course of a year. Patrick McGoohan was inspired to film his series there after filming a couple of Danger Man (1960) episodes in the village.
The building in Portmeirion shown as Number Six's house in the series became a gift shop selling Prisoner-related merchandise.
"Rover", the menacing white balloon that acts as a surreal sentry in The Village, was supposed to have been a large robotic machine. During the filming of the first episode, it was supposed to travel across water on a pair of rails hidden under the surface. The machine fell off the rails and into the water, damaging the motors inside. Just then, a weather balloon passed by, and Patrick McGoohan came upon the idea of "Rover" being a large white balloon that traveled by itself. The reason the cast stands still as Rover wanders past is because the balloon is being pulled by a wire. The shots were then run backwards, and edited into the film (In one episode, smoke can be seen drifting back into a chimney in the distance as Rover passes by). Impressively for a last-minute improvisation, Rover has remained disquietingly menacing and believably futuristic as a sentry drone while the surrounding technology in the series has dated noticeably over the decades.
Patrick McGoohan was adamant that Number Six not become romantically involved with anyone on the series (carrying over a policy he put in place for his John Drake character in Danger Man (1960)). Nonetheless, writers tried to pair Number Six up with female leads on a few occasions, only to have their efforts vetoed by Patrick McGoohan. The characters played by Nadia Gray in "Chimes of Big Ben" and Angela Browne in "A Change of Mind" were both written as love interests for Number Six, and there was reportedly a bed scene written for "Chimes" but McGoohan would have none of it. The closest Number Six comes to romance is in his friendship/simpatico with Alison in "The Schizoid Man" and in the character of an observer who falls in love with him in "Dance of the Dead."
At the end of the run of Secret Agent, there was a party, and some members of Parliament attended. Someone said to McGoohan, "So, what does a secret agent do when he retires?" meaning McGoohan. McGoohan took it literally and asked the question to some Parliament members. "Oh, we take care of them. We give them a house, a car, some pocket money, and that way they don't defect." This inspired McGoohan to create the show.
George Markstein: The bald-headed man sitting behind the desk during the opening credits is the series' script editor and co-creator.