The Filet-O-Fish was created to attract customers observing Catholic dietary rules.
Franchisee Lou Groen developed the sandwich in 1962 at a Cincinnati restaurant whose neighborhood had a large Catholic population. Sales traditionally weakened on Fridays, when many Catholic customers avoided meat, so Groen proposed a fish sandwich as an alternative.
The original product used a fried fish fillet, a bun, tartar sauce, and cheese. It gave McDonald's a branded menu item for customers who wanted a meatless option without leaving the restaurant.
The Filet-O-Fish is often described as a seasonal or temporary experiment, but it became a permanent part of McDonald's menu history. Its creation also illustrates how franchisees influenced the chain's product and branding development.