FDR, LBJ, JFK, MLK. Some people (typically men for some reason) are known by their 3 initials.
But what does it mean, if anything? Does it mean they have really arrived on the scene? Or that they are really near and dear in people’s hearts?
This is something I have literally wondered for decades.
I have to tell you, there is also ONJ–singer Olivia Newton-John, who just happens to have a long name. But that could just be one exception to the rule (-?).
:):)
Off the top of my head, I can only think of a couple more recent examples of well-known people who are sometimes known by three letters:
And, even then, it’s a stretch, as you have to include the J in “Junior,” or both the L and B in “LeBron,” to get to three letters.
There’s a new favorite - AOC (Alexandria Ocasio-Cortez). Yes we did have a recent thread where Dopers were all “wtf is AOC? IDK!” but trust me, that’s what people are calling her.
I dunno if it means she’s arrived. I think it might mean her name has too many syllables.
There’s football player RG3
A lot of the impetus for initials came from newspapers. Saved a lot of headline space: “LBJ signs law”.
Newspapers are not so influential anymore, they had quite a few short named Presidents after LBJ, etc., etc.
But initials are coming back thanks to Twitter and such. Hence “AOC”.
Let’s not forget RBG.
She is Notorious, after all. 
Don’t forget CNR.
I think this only happens to people who were initially (no pun intended) known by full 3 names.
It also helps if the initials are easy to say.
I know this isn’t what you were looking for, but the thread title triggered this memory, a quote (from memory, so forgive me if it isn’t exactly right), from the play Cyrano de Bergerac.
Cyrano: These are things that you might have said, if you had some tinge of wit or letters. But of wit, alas, you have none; and as for letters, it takes only three to write you down, A-S-S.
Note that the presidents after LBJ usually had short names: Nixon, Ford, Carter, Reagan, Bush, Clinton, Bush, Obama, Trump. All six letters or less (except for Clinton, but for typesetting purposes, the “li” combination counts as one letter).
And for Clinton you have HRC. Also there’s QE2. Thatcher could have been abbreviated to MHT but wasn’t.
There’s a guy at work who is referred to by his three initials (hyphenated last name, like Ocasio-Cortez). I think it’s because that’s how he would sign off on his emails.
Was FDR the first well known person to be commonly referred to by three initials? Interestingly, his distant cousin Theodore was frequently known as “TR,” possibly because of the length of his last name. Was he the first president to commonly go by his initials?
Edward M. Kennedy, unlike JFK and RFK, rarely if ever was called EMK, instead going by “Ted.”
Andrew Lloyd Webber gets written up as ALW, which takes up a lot less space than his last names “Lloyd Webber.” And his brother Julian is JLW.
and three letters and a name
W. E. B. Du Bois-sociologist
P. G. T. Beauregard-Civil War General
W. E. B. Griffin-writer
Was he actually called this as president? It looks like he signed communications as “TR,” but was that known to the general public at the time? The New York Times doesn’t
seem to have used it while he was president.*
But there really wasn’t any need to abbreviate before FDR. Starting from 198, you had Taft, Wilson, Harding, Coolidge, and Hoover. All relatively short names. Roosevelt became FDR to save headline space. Truman was a short name. Eisenhower was long, and he became “Ike.” When TR was president, headlines were smaller and a longer name was just printed.
*Maybe not the best example: The Times refused to use “Ike” for Eisenhower and set up a special bit of type to fit his name in.
Not exactly on point, but this thread brought this to mind: The Land of the Three Name People
Nonetheless it happened, as with the nickname “OK” = “Old Kinderhook” for President Martin Van Buren in 1840. Although, as the Perfect Master has explained, this was not the ultimate origin of the term “OK”, I’d say it does count as a Presidential abbreviation.
(Hijack: There’s an absolutely fascinating although severely incomplete Wiki page of US Presidential nicknames.)
I guess if you’re willing to count Christograms, that tradition goes back quite a bit further.
I’m sure there were, for example, famous generals and authors popularly referred to by their initials before FDR’s day, but can’t instance one off the top of my head.
Normally, it is journalists that give these acronym names to politicians, celebrities, and athletes, not the general populist. These editorial shortenings are a way of being efficient in print space and speech time. The general pop then adopts these acronyms and makes them popular.