The Filet-O-Fish was introduced by McDonald's in 1962 to attract customers who avoided meat on Fridays, especially during Lent.
Franchisee Lou Groen developed the sandwich in Cincinnati, Ohio, where his restaurant served a large Catholic population. The original product used a fried fish fillet, cheese, and tartar sauce on a bun. Its sales demonstrated that a carefully targeted menu item could expand the audience for a standardized national brand.
The Filet-O-Fish is a branding milestone because it established a recurring McDonald's pattern: a consistent core identity supported by products that respond to cultural and regional eating habits. The sandwich became a permanent menu item even though its original sales challenge was seasonal.
It is sometimes confused with McDonald's later seafood promotions or with the McLobster, a regional Canadian sandwich. The Filet-O-Fish is the older, enduring product and is strongly associated with McDonald's Lenten advertising and menu history.