There is an entire paper looking at the history, meaning and cultural significance of the foo, bar, baz words: https://link.springer.com/article/10.1007/s13347-019-00387-2

Smokey Stover, the 1935 "Where there's foo, there's fire" guy, was a TV cartoon in the 1970s. https://en.wikipedia.org/wiki/Smokey_Stover#Animation Influenced by german furchtbar/foobar/fubar, MIT used fu() and bar() in the late '30s.