My father's middle "name" was a single letter. My grandparents didn't give him a middle name (at least not in English), but the nurse took it upon herself to record what sounded like a middle initial to her, and that's what ended up on his birth certificate. It stood for nothing but the letter itself.

I love it when I get asked that as a security question, only to be told it's invalid (too short). Tell that to Harry S Truman!

https://en.wikipedia.org/wiki/Harry_S._Truman#Boyhood_and_fa...