Filet-O-Fish was the product name created for a fish sandwich introduced by McDonald’s franchisee Lou Groen in 1962.
Groen operated a restaurant in Cincinnati, Ohio, where many customers observed meatless eating on Fridays. He developed a fish sandwich to attract those customers, and McDonald’s tested the product against a ham-based alternative. The Filet-O-Fish won the test and became a permanent menu item.
The sandwich originally used halibut before McDonald’s later standardized the fish supply around other species, including pollock. Its branding combined the familiar “Filet” term with “O-Fish,” giving the item a distinctive name within McDonald’s naming system.
The Filet-O-Fish is often described simply as a Lenten product, but its creation was also a response to local customer patterns. Groen’s franchise-level initiative became a nationally recognized part of McDonald’s menu history.