The Jargon File (version 4.4.7, 29 Dec 2003):

Bloggs Family
 n.

    An imaginary family consisting of Fred and Mary Bloggs and their children.
    Used as a standard example in knowledge representation to show the
    difference between extensional and intensional objects. For example, every
    occurrence of ?Fred Bloggs? is the same unique person, whereas occurrences
    of ?person? may refer to different people. Members of the Bloggs family
    have been known to pop up in bizarre places such as the old DEC Telephone
    Directory. Compare Dr. Fred Mbogo; J. Random Hacker; Fred Foobar.