Explanations/etymology also appreciated!
For Joe Shmoe, it means a very average or below average person. It’s a derivation of the practice of using “shm-” to dismiss something (eg “Practice shmactice. We’re already perfect”).
And “John Smith” is meant to be the most average name or person imaginable, so they have the “most common” (citation needed) first and last name as well.
Some others in the Anglosphere:
Fred Bloggs - no idea where it’s from. Related to “bog” as in bog standard maybe?
Tom, Dick and Harry - is ages old. Even as far back as Shakespeare you can see the triplet evolving. “Tom, Dicke, and Francis” : Henry IV, Part I
I’ve always heard it as Joe Bloggs. The Bloggs bot is believed to be a derivation of bloke
Australian here, Joe Bloggs is very common here.