In the U.S. we often use the names John Doe and Jane Doe to refer to an unknown male or female, and John Q. Public to refer to any generic citizen. Other North American names include Joe Sixpack and Joe Schmoe (used in a somewhat derogatory sense).
Naturally, other countries use different names to the same effect, and I found it a fascinating list. For example, how about these?
- United Kingdom Joe (or Fred) Bloggs
- Malta Joe Borg
- South Africa Koos van der Merwe or Piet Pompies
- Sweden actually uses "Name Name" as a placeholder
Even times and dates can have placeholders, such as Juvember (an indeterminate month) or "Oh-dark-hundred" (some unreasonably early hour) and perhaps my favorite "(God's)-Ass-o'Clock," a nonexistent time that refers to the wee hours of very early morning. The word "God" may be omitted depending upon user's preference.
Speaking of "John Doe", one of the founding members of the long-lived Los Angeles punk band X is named... John Doe.
Here they are in 2008 playing their 1983 classic "The New World": John Doe, Exene Cervenka, Billy Zoom, D.J. Bonebrake, better known as X.