John Doe.
Joe Schmoe.
Ploni ben Ploni.
When the Gemara needs a placeholder name but doesn’t want to use a real one, apparently it uses the name פלוני (transliterated here as Ploni). Ploni can be used both as a person’s name as well as a name of a place.
In mock contracts, sometimes the formula פלוני בן פלוני במקומ פלוני (Ploni ben Ploni b’Makom Ploni) is used. This translates rougly as “Ploni, son of Ploni, from the city of Ploni.”
Delightful. I remember finding it equally amusing a few years ago when I learned that French programmers don’t name temporary variables foo or bar, but rather toto and tata.