During WWII there was a popular comic strip about a fireman called Smokey Stover. The backgrounds were filled with all sorts of silly puns and nonsense references. The word "Foo" showed up as a catch-all piece of gibberish in the most unexpected places and contexts.

Therefore the mysterious "planes" which couldn't be attributed to any known source were either "bogies" or "foo-fighters." Hence the name of Dave Grohl's post-Nirvana band.

And of course Magnus ⚠️ ↗ was drawn by the great Russ Manning whose work on the Tarzan comic strip was IMHO better than the much lauded Burne Hogarth. In Europe, Manning is still thought of as THE Tarzan artist.

Dante