The Filet-O-Fish was the McDonald’s sandwich created in response to demand for a fish option.
Lou Groen, a McDonald’s franchisee in Cincinnati, Ohio, developed the sandwich in the early 1960s. His restaurant served a large Catholic population, many of whom avoided meat on Fridays, especially during Lent. Groen proposed a fish sandwich to address the resulting drop in Friday sales.
The sandwich originally used a breaded fish fillet, tartar sauce, and cheese on a bun. McDonald’s tested it alongside a meatless sandwich proposed by Ray Kroc, and the Filet-O-Fish became the successful choice. It was introduced nationally in 1965.
The product is a branding milestone because it expanded McDonald’s identity beyond hamburgers. Its name also made the main ingredient immediately clear, helping the sandwich remain recognizable across changing menus.