The Filet-O-Fish was created for McDonald's customers who wanted a fish sandwich.
Franchisee Lou Groen developed the sandwich in 1962 at a Cincinnati restaurant where many customers observed meatless Fridays. McDonald's added the Filet-O-Fish nationally in 1963, giving the chain a distinctive non-beef menu brand.
The product is often remembered only as a seasonal religious option, but its branding significance was broader: it expanded McDonald's identity beyond hamburgers and created a recognizable fish offering.
The sandwich's name, fish-shaped packaging in some periods, and long-running advertising helped make it a permanent part of McDonald's menu history.