The Filet-O-Fish was introduced by McDonald’s in 1962 to attract customers who ate fish on Fridays.
Franchisee Lou Groen, who operated a restaurant in a heavily Catholic neighborhood of Cincinnati, developed the sandwich after noticing weaker Friday sales. During Lent, many Catholic customers avoided meat on Fridays, creating a business problem for a restaurant whose menu centered on hamburgers.
The sandwich used a fried fish fillet, cheese, and tartar sauce on a bun. McDonald’s tested it against a meatless alternative before choosing the Filet-O-Fish for wider sale. Its name clearly communicated the product’s main ingredient while fitting the company’s compact naming style.
The item’s origin is often simplified as a general seafood innovation. More specifically, it was a franchisee-led response to local religious eating patterns and was later adopted across the McDonald’s system.