The names "Joe Bloggs" and "Fred Bloggs" are commonly used as placeholder names in the United Kingdom, Australia and New Zealand, for teaching, programming, and other thinking and writing. The surname Bloggs on its own is sometimes used in the same way. Fred alone can be a programming placeholder (due to its letters being close together on the standard QWERTY keyboard).
Other placeholders (e.g. in advertisements for store cards/credit cards) sometimes used are Mr/Mrs A Smith or A. N. Other. In the United Kingdom and United States, John has historically been one of the most common male first names, and Smith is the most common surname in each, so "John Smith" is a recurrent pseudonym and placeholder name in those countries (especially in legal contexts).
In the United States, John Doe, John Q. Public, Joe Blow, Joe Sixpack and Joe Schmoe are also used. In Germany, Max Mustermann (male), Erika Mustermann (female), and Otto Normalverbraucher are used. Other international variations can be found here.
