One of the reasons for this series being set in Hawaii is that CBS did not want to close its Hawaii production offices when Hawaii Five-O (1968) ceased production in 1980. This show started production that same year and contains occasional references to Steve McGarrett and "Hawaii Five-O", although McGarrett was never shown.
According to Tom Selleck when he was interviewed for "Bravo TV's Countdown of the 100 Greatest Television Characters" his character, Thomas Magnum, was initially very different than what he became. He said originally Magnum was written as a "James Bond of television, visiting stewardess on each arm, flawlessly perfect" kind of character, which Selleck hated (by his own admission, he told the writers and producers "I'm tired of playing what I look like"). When asked what he wanted to do, Selleck remembered how much fun he had working with Jim Garner on "The Rockford Files" and remembering how envious he was of the Rockford character as opposed to his own, suggested they make Magnum more of a laid back, blue collar "average joe" jock slob that men could identify with (his rational being that if men watched the show and were able to identify with him, it would bring in even more male viewers. After refusing at first, to which Selleck threatened to go do Raiders of the Lost Ark instead, the writers and producers backed down, and as a result, Magnum became the approachable, love able, charming jock type character he would be famous for.
Magnum was a Vietnam War Veteran. At the time the series began, the war and it's aftermath was still very much a controversial issue. Magnum (along with TC and Rick) have been cited as among the first positive portrayals of Vietnam Veterans on a Network TV series.
Just prior to Magnum, Tom Selleck played a recurring role on The Rockford Files. Producers had wanted to do an episode of Magnum in which James Garner guest starred as Jim Rockford, but were unable to due to rights issues.
Episode #149 (7.22) Limbo, where Magnum was to be shot dead by mobsters was to be the CBS series finale on 15 April 1987. When the show's fans heard this, there was a huge public outcry and the "shot dead" plotline was nixed by the producers. Magnum was indeed shot by mobsters in this episode. Magnum returned for an unprecedented 8th season on CBS, filming 12 more episodes.
When Frank Sinatra agreed to do a guest part on the show, producers sent Sinatra a list of story ideas they were considering and Sinatra chose the idea he wanted to do. The story he chose was called "Laura" and it ran during the seventh season.
In the first episode, Rick was owner of a club called 'Rick's Cafe Americain', and played a Humphrey Bogart wannabe. After's the Cafe's demise, Rick became manager of the King Kamehameha Club. T C always referred to Higgins as "Higgy Baby".
Tom Selleck is a big Detroit Tigers baseball fan. Several episodes feature references to the Tigers. When they won the World Series during the run of the show, tentative plans were made to film an episode in the Detroit area but those plans were scrapped.
Magnum's full name was Lieutenant Thomas Sullivan Magnum IV, USN (the two gold stripes on the shoulder-boards of his dress whites indicate he was a Lieutenant, if he was a commander he would have three stripes). His father, Commander Thomas Sullivan Magnum III, USN, was a Naval aviator killed in Korea, and is seen in flashbacks (played by Robert Pine). His grandfather, Captain Thomas Sullivan Magnum Jr, USN, (played by Howard Duff), is seen in the 8th season episode "Resolutions." His great-grandfather, Thomas Sullivan Magnum, is seen in a home movie watched by Magnum and his nephew in the 6th season episode "Going Home."
On his navy uniform, one can see the blue and white ribbon for the navy cross, as well as the naval special warfare insignia. This means he earned the nation's second highest award for naval personnel and was a SEAL.
The multicolored helicopter used by Magnum's war buddy T. C. for his Island Hopper charter service was a Hughes 500. This is a commercial variant of the Hughes OH-6 Cayuse developed for the U. S. military. Several different helicopters were actually used during the run of the series including both D series (T-tail) and C series (Y-tail) varients.
At some point during the run of the series, Magnum has the distinction of being punched, at least once, by each one of his friends: Higgins, Rick, and T.C. However, Magnum never struck any of them at any time.
Higgins has four illegitimate siblings, all sharing the same father but different mothers: Father Paddy McGuinness, an Irish priest; Soo Ling, a half-Chinese sister; Elmo Ziller, a rodeo owner from Texas; and Don Louis Mongueo, a royal heir to the throne of Costa De Rosa in South America.
Soon after Magnum PI ended, there was some interest on Universal's part on doing a theatrical film with the original cast, and a script was written by Tom Clancy dealing with Magnum returning to the Navy and his subsequent adventures. However, Universal ultimately felt that the original cast and Clancy's script would not be a big enough draw at the box-office and passed.
A few episodes were written (or re-written) to focus mainly around one or more of the show's secondary characters. This was done to accommodate Tom Selleck, who as the result of being cast in some feature films, was at times unavailable to film full episodes.
Thomas Magnum's weapon of choice is the Government model Colt 1911 A1 .45 cal. Automatic pistol which, when need arises, he usually carries tucked into the waistband of his pants in the so called Mexican carry fashion. As the Colt 1911 A1 was the standard U.S. military issue pistol during the Vietnam era, it can be assumed that this was his personal sidearm from his service as a Navy seal in that conflict.
The recurring character who made the most appearances was Higgins female companion Agatha. Agatha was played by Gillian Dobb who has no professional acting experience outside of Magnum. Like John Hillerman, Dobb was American despite her character being British.
This drama series was one of the highest rated shows on Thursday nights until the debut of The Cosby Show (1984) sitcom. The sitcom eventually became the #1 show on the air and routinely out-rated Magnum.
Higgins was actually a baronet, a British hereditary noble. He was engaged to a countess, but she broke it off when he refused to renounce his title; she didn't want to take a step down in the heraldic list. When Robin bought a castle in England and set the crew to get things set up, Higgins refused to see his father (they were estranged over Higgins' dismissal from Sandhurst), so Magnum 'kidnapped' Higgins and drove him to the family estate, where he was embraced by his father, also played by John Hillerman.
Throughout the series, it was made clear that TC abstained from drinking alcohol. Oddly enough, a scene of him in the pilot raising a bottle of beer was shown for many seasons during the opening credits.
The episode "Echoes of the Mind" (which guest-starred Sharon Stone) opens with the New American Orchestra's version of the Blade Runner (1982) theme on the soundtrack. At the time, this was the only version of the "Blade Runner" theme legally available.