TIL that the “S” in “Harry S. Truman” isn’t an abbreviation. His middle name was just “S”.
TIL that the “S” in “Harry S. Truman” isn’t an abbreviation. His middle name was just “S”.

Harry S. Truman - Wikipedia

TIL that Harry S. Truman, the 33rd president of the United States, had no middle name. His middle initial “S” was not short for anything, but was chosen to honor both of his grandfathers, Anderson...
There's also Ulysses S. Grant. The "S" was apparently just a mistake on his enrollment at West Point. His birth name was Hiram Ulysses Grant. He tried to switch his first and middle names, but ended up with the initials USG instead of UHG.
https://www.britannica.com/biography/Ulysses-S-Grant
And then there's the odd case of "Thomas a Becket." Thomas Beket was never called Thomas a Becket in his lifetime. He apparently went by many names, one of which was "Beket," but never "a Becket."
https://www.york.ac.uk/news-and-events/news/2023/research/thomas-a-becket-study/
Is this the genesis of British "humour"? Thomas, a Becket, even got the name in the time of Shakespeare.
Waiting for somebody to eviscerate me over British history, cause all I know is Monty Python.
Yeah, that's just odd. 'A' isn't something you'd find before a surname as part of the name, unlike 'd' or 'o' etc.