According to the DVD commentary, neither Sir Roger Moore, an uncredited co-Producer, nor Robert S. Baker, the credited Producer, ever had a contract, other than a handshake with Sir Lew Grade. They produced the entire twenty-four episodes without a single written word guaranteeing that they would ever be paid.
Throughout the series, Danny Wilde (Tony Curtis) is almost always seen wearing gloves. According to DVD commentary, this was a gimmick developed by Curtis, to make his character unusual, and therefore create some buzz for the series.
In France, this show was wildly popular because it was dubbed in an irreverent way, ad-libbing a lot, thus departing from the original scripts, and using very funny, often absurd colloquialisms and phrases. Because of that, in France, it had more of a comedy element to it, more so than its original version, making the characters even more quirky and lovable. The French dubbing is, understandably, largely the reason for this show's success and popularity in France. (The same thing happened there with the dubbing for Starsky and Hutch (1975)). Other countries in Europe, such as Spain, followed the France model.
The most ubiquitous firearm used in the series is a Model 1934 Beretta in 7.65 Browning, a.k.a. .32 ACP. It appears in almost every episode involving a handgun. When a revolver shows up, it is almost always a Colt Detective Special.
Popular in Denmark, and still repeated on television forty years after. The Danish title "De uheldige helte" (The Unlucky Heroes) plays with the words held=luck and helt=hero. The title tune was also a bit of a hit.
Other countries such as Switzerland, Austria and even West Germany followed France's lead---where it is worldwide known to be more famous than in USA---in dubbing the series in an unconventional way, using very funny, often absurd expressions and phrases. Because of that, like in France, it became very popular (unlike the English version) and, as in France, is still regularly repeated on German television. Tony Curtis had asked Rainer Brandt , the West German speaker, to write the dialogue for the next season, but the series got canceled before this could happen.
The filmed sequences, presenting Danny Wilde and Brett Sinclair, in the opening credits, were not filmed expressly for said credits, but were taken from various early episodes (all of them in the French Riviera), mainly The Persuaders!: Overture (1971) (the two men racing their sports cars, Tony Curtis and Sir Roger Moore distracted by a blonde in a bikini walking between them, Brett flirting with two beauties) and The Persuaders!: Powerswitch (1971) (the water-skiing shots, and Danny shown as a businessman at work at a desk).
Sir Roger Moore and one-time guest star Dame Joan Collins commented on Tony Curtis' heavy marijuana use, which lasted throughout the series' run. In fact, before the show was to begin shooting its first episode, Curtis was arrested at England's Heathrow Airport for possession of cannabis.
Tony Curtis was born Bernard Schwartz of Jewish-Hungarian immigrants, and if you pay attention, you will find him sprinkling inside jokes to his origins throughout the series. In The Persuaders!: Greensleeves (1971), for instance, his character pretends to be Brett Sinclair's new butler, Grzegorz (Gregor), and explains his (fake) east European accent by his being from a "Hun-GAA-rian" from "BU-dapesht" (unfortunately for Danny Wilde, the black beauty from an African republic, with whom he shares this, speaks the language perfectly). Torn from his Paris hotel shower in The Persuaders!: The Old, the New, and the Deadly (1971) by the telephone ringing, which turns out to be a wrong phone number, a dripping wet Danny states, "No, this is not Mr. Schwartz, you got the wrong room!"
Originally, the title was going to be "The Friendly Persuaders". But, because that sounded too close to Friendly Persuasion (1956), it was shortened. Coincidentally enough, in France, the title "Amicalement vôtre" translates to "Friendly yours", or "Yours, amicably".
In episode fourteen, "The Man in the Middle", Brett Sinclair accidentally dropped his passport during a fight in the first scene. As part of the plot, it is picked up by MI5 Agent Kay (Suzy Kendall), and opened at the photo page in close-up. Lord Sinclair's place of birth is clearly stated as "Scotland".