A waiting room I was in had a very old copy of People featuring Heidi Montag, and now there are so many teenagers who will never understand who she was or why she was so famous. I’m curious to take a trip down memory lane and remember all those celebrities who used to be so important.
Burt & Loni.
Farrah and Lee. Of course Farrah is dead now but she never reached that level of saturation that she did then.
Cyndi Lauper
I was stunned when my cousin’s kids had no idea who Clark Gable was. He was just a little bit before my time, though.
About 25 years ago, I met a couple of teenagers who thought that Mel Brooks was the voice of Bugs Bunny. I might have been slightly impressed by the fact that they confused him with Mel Blanc, except that Blanc’s death had been in the news not too long before.
I had to look up Heidi Montag, as I vaguely recognized the name, but had no idea who she was. Reality TV stars are, generally, among the most ephemeral of celebrities, save for the very few who managed to leverage it into something bigger. So, I don’t find it surprising at all when their fifteen minutes of fame evaporate.
A lot of the people who were celebrities when I was growing up aren’t in the public eye any more, largely because they’re dead or retired. 
Not really sure what the OP is getting at. Lots of the celebrities from my youth are retired or dead. Names like Tony Randall, Paul Lynde, or Christopher Lloyd might be losing hold on the public consciousness, but people of the present day would understand if we said they were in movies or TV. Are we looking for the inexplicably famous for being famous?
Charo
Art Linkletter
Susan Sontag
What exactly did you do with that poster? :eek:
Really? I still see her doing concerts and popping up on talk shows so, while she’s not as omnipresent as she seemed to be in the 80s, it’s not like she’s dropped off the face of the earth. A better example from the 80s would be Shelley Long (who, to my chagrin, I used to have a bit of crush on). In terms of where she was fame-wise when she left “Cheers”, her career has fallen the hardest compared with the other cast members of the show. Even John Ratzenberger (Cliff) is still active doing Pixar movies and occasional guest shots.
Shaun Cassidy was all over the place when I was growing up. Is he dead now?
She also won a Tony in 2013, for her score for “Kinky Boots,” and has been a prominent activist for LGBT causes.
Nope. He moved into stage acting, then writing and producing TV series. He’s still very active, but on the other side of the camera.
I am, I suspect, older than you, since I had no idea who Heidi Montag is, and it certainly ain’t because I’m too young. 
My contribution: For about two years in the late 1970s, one of the hottest entertainment acts in the country was the husband and wife mime team of Shields and Yarnell. Apart from Marcel Marceau, it may be difficult to imagine a celebrity mime act. But trust me, for awhile there, Shields and Yarnell were everywhere. They guest-starred on everything from The Muppet Show to The Tonight Show to Wonder Woman, performed for presidents and Queen Elizabeth II, and even had their own variety show for about a month. But who remembers them now?
All celebrities will fade from the public consciousness eventually. But Shields and Yarnell are the only ones that I look back on from my childhood and wonder how they managed to get so famous in the first place. It’s hard to imagine an act like that getting that sort of attention today.
I don’t believe I ever heard of Heidi Mnotag, and after a google search, can confirm that.
“So famous” doesn’t seem to be accurate for this woman. “Sort of famous” maybe.
Still, I’ll play:
Alan Alda and Mary Tyler Moore.
Rick/Ricky Schroeder, who is now playing Dolly Parton’s father in her movies.
Raymond J. Johnson Jr, was the one I found most hard to fathom how fame was ever achieved. S & Y, did have a talent, not one most would find entertaining, but they were good mimes.
But.
You don’t have to call me Johnson, You can call me Ray, or you can cal me J, you can call me RJ… etc ad nauseam, But you doesn’t have to call me Johnson
Patricia Hearst
Bobby Riggs
Julie Nixon and David Eisenhower
Donovan is appearing at our local PAC next week. He was all over the place in the 1960’s, hailed as the new Dylan. I was amazed when I realized how long its been since I heard anything about him.
Has anyone ever done a better disappearing job than Johnny Carson after retirement?
Morton Downey, Jr. (dead, I know, but still)
Morganna the Kissing Bandit
Charo
Phil Donahue
mmm
I was going to suggest Alan Alda. I mean, I will always love him and follow his career, which more recently has included a role on The West Wing, hosting Scientific American Frontiers, and writing several books, but I’m fully aware that he isn’t known the way he once was.
Back in the mid-seventies, pre-Internet, People Magazine used to have an annual readers’ poll about celebrities. After the first few years, they had to change the format of the questions like this:
Other than Alan Alda, who is your favorite actor?
Other than Alan Alda, what celebrity would you most like to have dinner with?