Filet-O-Fish was launched in 1962 as McDonald's first menu item designed for Catholics observing Lent.
The sandwich was created by franchisee Lou Groen in Cincinnati, Ohio, where many customers avoided meat on Fridays during Lent. Groen proposed a fish sandwich to attract those customers without abandoning McDonald's core hamburger business.
The product was initially tested against a meatless competitor, the Hula Burger, which used a grilled pineapple slice. Customers preferred the fish sandwich, and McDonald's expanded the Filet-O-Fish.
The product became an enduring McDonald's brand and is still associated with the chain's seasonal Lent advertising. Its name is a direct compound of “filet” and “fish,” unlike later product names that emphasized the McDonald's “Mc” prefix.