The Only Gilligan's Island Actors To Appear In Every Episode
There are some sitcoms that simply don't work if you're down so much as a single cast member. Could you imagine an episode of "Cheers" without Sam, Carla, Cliff and Norm? The series' producers and writers couldn't, which is why they never missed an episode. The same was true on a much larger scale for "The Brady Bunch," where every single member of the family (and their live-in housekeeper Alice) reported for duty on all 117 episodes.
This kind of consistency was evidently key to a successful Sherwood Schwartz sitcom. The writer/producer who created "The Brady Bunch" was also the mastermind behind "Gilligan's Island," the CBS joker about seven castaways who wash up on the shore of an uncharted island somewhere in the Pacific Ocean. The key to the show's success was its shamelessness: from the pilot to the series finale (which arrived a little sooner than expected thanks to "Gunsmoke"), you could count on seeing every member of the ensemble engage in all manner of inanity (just like you could rely on them remaining on that island, no matter how hard they tried to escape, by the time the end credits rolled).
Schwartz wasn't one to deviate from formula, but he was wise enough to know early on in the show's run when an actor he'd cast wasn't clicking with their co-stars. How early? Try the pilot, which is the only episode of "Gilligan's Island" that didn't feature three of the show's most beloved actors.
Why did three of Gilligan's Island's castaways miss an episode?
If you've never seen the "Gilligan's Island" pilot, it's actually worth watching if only to see just how utterly wretched the series could've been with a miscast Professor, Mary Ann, and Ginger. Yep, Russell Johnson, Dawn Wells, and Tina Louise were not the first choices for the roles that wound up getting them typecast for the rest of their careers.
One significant issue was that the parts were poorly conceived and written. Initially, Schwartz had cast John Gabriel not as the Professor but as a high school teacher. As for the plucky, very on-the-ball Mary Ann, she was named Bunny and played as a shallow blonde by Nancy McCarthy. As for Ginger, the red-haired movie star was a snarky secretary portrayed by Kit Smythe. It's hard to judge these three fairly since we've only ever known Johnson, Wells, and Louise, but they're just bad complements to Gilligan (Bob Denver), the Skipper (Alan Hale Jr.), and the Howells (Jim Backus and Natalie Schafer).
So now, when you hit up the "Gilligan's Island" page on IMDb and notice that the aforementioned trio comes up one episode shy of 99, you'll know why. Keep that info on the DL, though; you never know when it might be a pub trivia question.