Banned Episode / Missing Episode: "Bored She Hung Herself", a 1970 episode about a deadly yoga technique that bears more than a passing resemblance to Erotic Asphyxiation, has been banned since its original broadcast, allegedly because a viewer accidentally died while imitating the technique. The episode was never syndicated, and it's not included on the second season DVD box set.
Directed by Cast Member: Jack Lord, of course; in addition to directing six episodes he was also more or less an uncredited executive producer (especially after creator and actual EP Leonard Freeman passed away in 1973).
Wo Fat, played by Anglo-Egyptian-Sudanese-American Khigh Dheigh. Yes, really.
Mexican actor Ricardo Montalban gets it twice: as the Japanese Tokura in "Samurai" and as European race car driver Alex Pareno in "Death Wish On Tantalus Mountain". At least they weren't in the same season (although seeing these episodes back-to-back in reruns can be jarring...).
Mark Lenard, alias Sarek, played a Japanese saboteur in "To Hell With Babe Ruth." Oh dear.
Fictional Counterpart: Averted. There has never been a "Five-O"-like police agency in the history of Hawaii. Reportedly, phone books advised tourists to dial 911 instead of trying to find the number to Five-O.
The Other Darrin: Tim O'Kelly as Danno, Lew Ayres as The Governor and James Gregory as State Department official Jonathan Kaye (a recurring character on the series) in the pilot movie; Ayres later guested on the series (twice, in different roles), as did pilot cast members Andrew Duggan (four times!) and Leslie Nielsen. Kaye, meanwhile, was played by a total of six different actors.
Similarly, Albert Paulsen played villain Charley Bombay in season two's "Just Lucky, I Guess"; when the character returned in season eight's "McGarrett Is Missing" he was played by Charles Cioffi (making him The Danza). He also had his name slightly changed to Charlie.