After the original Hawaii Five-O ended its run in 1980, CBS promptly picked up another crime drama to be set in the same general area.
Magnum, P. I. put producer Donald Belisario on the map, as he would later shepherd shows like JAG, also for CBS, and Quantum Leap for NBC. Tom Selleck was cast as Thomas Magnum IV, a former Navy man who now was a private eye operating out of Hawaii. His base of operations was the island estate of reclusive millionaire Robin Masters, who was heard, but rarely seen (Orson Welles provided the voice-over in several episodes, but a different actor essayed the part when Masters was, ah, brought to life near the end of the run). Instead, Masters' major domo, John Higgins (John Hillerman, ex-Ellery Queen), ran the joint, and at one point, Magnum was led to believe Higgins & Masters were one and the same. Of course, that wasn't true.
In a classic moment, Magnum paid homage to Hawaii Five-O during the first season, and the remake of Five-O would later return the favor. There were crossovers with other Universal series, including Simon & Simon and Murder, She Wrote, but the Magnum half of the latter crossover was re-edited for DVD release, rather than shoehorn a Murder episode in the appropriate season set for continuity purposes. In all, Magnum ran for 8 seasons, and of course found new life in syndicated reruns during the 90's.
Today, Selleck stars in another CBS drama, Blue Bloods, but Universal has accepted an offer from another producer to do a sequel, this one involving Magnum's daughter, who had followed in her dad's footsteps as a Naval investigator before turning to the life of a P. I.. However, this version is ticketed for ABC instead of CBS. Go figure.
Here's the intro everyone knows, with the pulsing theme by Mike Post & Pete Carpenter.