A lengthy report on the "Etymology of Foo" has been published as rfc3092.

Although it is likely that FUBAR helped bring "bar" into use as the second metasyntactic¹ variable, "foo" existed prior to WWII. It's first known recorded use was in the Smokey Stover comic strip by Bill Holman, but it also showed up in a Warner Brothers cartoon and Pogo by Walt Kelly.

1. They are called "metasyntactic variables" because they are used as variables for variables in code examples.

-sauoq
"My two cents aren't worth a dime.";