Let us not forget ‘Diane’ from ‘Twin Peaks’. If she appeared later in the show I never saw it.
I personally never watched the show (though SNL’s parody was so hilarious!), but did the audience ever see “Diane” from Twin Peaks?
-Joe
A fairly obscure one, but as I recall we never saw anything but the back of the head of Evie’s alien father in Out of This World (and that was just in the flashbacks in the credits each week):
We never got a good look at Spot on THE MUNSTERS.
On the COSBY SHOW, Rudy’s buddy Kenny (“Bud”) hero-worshipped his older brother to death and parroted him endlessly on women and music. But not only did we never see Kenny’s brother in ten years on the show – I’m pretty sure we never even learned his actual name. That’s pretty freaking invisible.
We never saw Claire’s rival for Cliff’s affections, Eunice Shantilly, either. We also learned that Cliff (like the real life Cos) had a brother named James, who died in childhood and prompted him to become a doctor. We obviously never saw the character nor did we hear about him again.
For years on **THE JEFFERSONS ** their upstairs neighbor Mr. Whittendale was talked about but never seen but I seem to recall their ruining that.
We never get to see Mr. Bloodhound on The Bloodhound Gang.
I don’t know if this counts, but on Invader ZIM, we never see Dib & Gaz’ mother (do they have one?). Also, we never Professor Membrane’s face.
As for Magic Voice on MST3K: she was performed by several cast and crew members including Mary Jo Pehl (Pearl Forrester) & Bridget Jones (Mike Nelson’s wife, who also did a few bit parts including Mr. B Natural and Lisa Loeb).
Sheridan from Keeping Up Appearances.
Why do I remember an episode where we meet The Gooch and he turned out to be a girl.
According to the TV Tome entry, the Gooch is never seen and is a boy.
Perhaps you are thinking of the episode where Arnold is doing a journalism course, and he writes an exposre of drug use in the school - the dealer is an older schoolgirl. Nancy Reagan also appeared in the episode.
Beating heart not withstanding, doesn’t someone have to be alive to qualify as an invisible character? Do you actually want them to dig up his grave to get a look at the guy?
The Triumverate on The Pretender. Well, we did learn the identity of one of the three, but only because he wore the right shoes.
That was, IMHO, the funniest. MASH. Ever!!! Come to think of it, it foreshadowed MST3K, with the smart-alecky voice-overs being far superior to what was actually intended by those in the film. IIRC, Col. Blake watches the film with them too, doesn’t he?
I loved Morn! I always thought that the very last line in the very last scene of the series should have been him saying, “Goodbye.”
Probably the ONLY funny sketches on that show in the last 10 years!
He actually had at least 3–there was Reba, who lived in the oven and only said “Rebe!Reba!”, and of course, Soupy’s two dogs, White Fang and Black Tooth (you only saw one of their paws). Greatest kid show in history, IMHO.
In “Ed, Edd, and Eddy”, Eddy (squashed pink head, green tongue, gold bowling shirt with a red stripe; always trying to scam the other kids in the cul-de-sac out of their quarters) has an older brother, admired by all in the neighborhood, who never shows up.
Can’t believe this thread is still going. Anyway, I don’t think anyone has mentioned the voice on the audiotape at the beginning of every Mission Impossible episode. “Good morning Mr. Phelps …”
I can’t believe this thread’s still alive either, but I’m likely to kill it. 
Having said that, on Maverick Bret and Bart’s dear old Pappy wasn’t seen for the first couple seasons of the show. Pappy was always quoted as having some offbeat bit of wisdom to pass along, like “Faint heart never filled a flush”, “If you can’t say something nice about someone then change the subject” or “A coward dies a thousand deaths, a hero only one. 1000 to 1 are pretty good odds.” In the third season there was an episode where the show’s star James Garner played a dual role as both Bret Maverick and as Beau “Pappy” Maverick.
British one: Mrs Ventrice in Heartbeat.
Off the top of my head, the only invisible character I can think of in an anime series is:
Sailor Moon - Lita/Makoto’s “old boyfriend” (I think he appers in a flashback from the neck down, but otherwise he is always referenced to when Lita becomes infatuated with a new guy - “he reminds me of my old boyfriend”.)
But in a lot of other anime, if the main character’s parent(s) are deceased, they’re usually not shown very clearly in pictures of them.