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.
Don’t forget his wife, Erika Mustermann, geb. (née) Gabler. She’s usually the one used for passports these days. I think there’s a whole Mustermann family living in these templates.
Isn’t it Erika Musterfrau?
Sometimes, but I mostly see her name as Mustermann.