Magnum, P.I., on CBS
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This aired for eight seasons, from 1980-88, though I'm not sure how much of it I saw. Thomas Magnum (Tom Selleck) lives in Hawaii on an estate which is owned by somebody named Robin Masters, whom we never see. The majordomo of the estate is named Higgins (John Hillerman), he's this British guy who often gets kind of annoyed at Magnum. I think some people think Higgins really is Robin Master, secretly. Or something. Anyway, Magnum is a private investigator. And he has a couple of friends, TC and Rick, who sometimes help him out. I'm afraid I don't remember it that well, but I liked it. If I ever rewatch it (which seems unlikely), hopefully I could write a proper review. But still, it's fairly nostalgic to me, and I liked the theme music.
A remake of the series began in 2018.