And now, the fish sandwich is an international sensation!
The Filet-O-Fish became the first addition to McDonald's original menu and has since become a staple of Micky D's menus around the globe, and inspired plenty of fast-food copycats. And on a micro-note, in Groen's words, it "saved his business."
The man himself passed away in 2011 at the age of 93, but his contribution to the world of fast food swims upstream eternally.
According to the original Cincinnati Enquirer profile on Groen, 23% of all Filet-O-Fish sandwiches are bought during Lent, and its religious significance has extended beyond Catholicism, as Muslims and Jews -- who also have dietary restrictions regarding meat -- have embraced it as well.
So the next time your Catholic guilt overwhelms you, and you opt for the Filet at the drive-thru on a Lenten Friday, thank Lou Groen and his spark of marketing genius.