Lou Groen created the Filet-O-Fish sandwich that became an important McDonald's menu brand.
Groen operated a McDonald's franchise in Cincinnati, Ohio, where many nearby customers observed Catholic dietary practices on Fridays. He developed a fish sandwich to attract those customers during a period when meatless meals were especially important to the local market.
Ray Kroc tested Groen's idea against a competing meatless sandwich at an early 1962 sales trial. The Filet-O-Fish performed better and was added to the McDonald's menu nationally later that year.
The sandwich is a product example of McDonald's branding history: a local franchisee's market-specific idea became a permanent international menu item. It is distinct from the company's visual logos and mascots, but it helped establish branded signature products.