McDonald’s introduced the Filet-O-Fish in 1963 to appeal to Catholic customers who avoided meat on Fridays. Franchisee Lou Groen developed the fish sandwich at a restaurant in Cincinnati, where the local Catholic population made Friday sales especially challenging.
The sandwich gave McDonald’s a meat-free option while preserving the chain’s familiar bun-and-topping format. Its original version used a fried fish fillet, cheese, and tartar sauce, establishing a recognizable product identity that McDonald’s continued to promote internationally.
The Filet-O-Fish is sometimes described as a response to general consumer demand for seafood, but its original business motivation was specifically connected to Catholic fasting practices and Friday traffic.