Actor-Shared Background: One of the only pieces of information Number Six voluntarily gives the Village is his date and exact time of birth (19 March 1928, 3:15 a.m.) — which coincides exactly with McGoohan's.
The Danza: Nadia in "The Chimes of Big Ben" is played by actor Nadia Gray.
Hey, It's That Guy!: If you watched Danger Man, chances are you're going to be doing this through the whole series as many people who played in Danger Man appear in various roles in the series.
Life Imitates Art: The official Prisoner fanclub's leadership dissolved in a heady mix of paranoia, backstabbing, and accusations of people spying on each other in real life. Several tertiary members mentioned this trope when they heard of what happened.
Recycled Script: "The Girl Who Was Death" is adapted from an unused Danger Man script, which is why it feels so much like a Danger Man episode, at least at first. This fact is also used as ammunition by those who believe No. 6 and John Drake are the same character.
Technology Marches On: Much of the technology, especially in "The General", have obviously become outdated. The big exception is the bulbous sentry robot, Rover, which still looks as believably advanced as a machine and scary as hell; not bad for a last minute improvisation when the intended prop sank.
Particularly fun these days is No. 6's aghast double take at a cordless phone in "Arrival."
Throw It In: Leo McKern was easily the most popular No. 2 among cast and crew, so they wrote new episodes just to bring him back. When the show was canceled, they rushed the final episode and added an on-camera haircut to "explain" his trimmed beard and shorter hair.
Troubled Production: The co-creators of the series, actor Patrick McGoohan and screenwriter George Markstein, almost immediately began to clash over what the series should be. George Markstein has gone on record stating that his idea for the series came about while McGoohan was making the spy thriller seriesDanger Man and that the premise would be about what if McGoohan's character, John Drake, resigned and was sent to a special resort-type prison similar of a kind used to crack POW's in World War 2. McGoohan on the other hand maintains that the two characters are different and that the two shows are completely independent. Beyond the question of the central character's identity, it seems that Markstein wanted to keep the series rooted in the espionage genre, with Number Six's character as a spy imprisoned by (probably) his own side because he knew too much, while McGoohan saw the show from the start as a much more abstract surreal allegory about the relationship between the individual and society. It is likely that both creators went into the project with their own notions of what the "truth" was, and both interpretations influenced the writing and the acting. Beyond the characterization many of the details of who created what and when were contested between McGoohan and Markstein, with the preponderance of the evidence supporting McGoohan, but not completely invalidating Markstein's claims nor his influences in writing the series. Once McGoohan won his power struggle with Markstein and the show started to get seriously freaky, Executive Meddling made things even more troubled. There are even conflicting claims from all concerned about how many episodes were originally planned, and whether the show was cancelled prematurely or not. Certainly, there are reports from many actors and crew members that the final episode, "Fall Out", was made in completely chaotic circumstances, with McGoohan still working on the script during recording breaks, Kenneth Griffith (who played the President) being asked to write his own dialogue and as much of the production as possible having to be recycled from previous episodes.
The original Rover was remote-controlled and resembled a giant wedding cake. Thankfully everyone realized how Narmy it would be (not to mention that the original model malfunctioned and shot into the sea, rendering it unusable), and happened to spot some weather balloons as they were discussing other possible designs.
Write Who You Know: Number Six is to an extent a stand-in for McGoohan, unsurprising given that the series is all about his own views on individuality and authority. A prime example of how Tropes Are Not Bad.