The Big Mac inspired McDonald's first national advertising campaign centered on a signature product.
McDonald's introduced the Big Mac in 1967, and its distinctive two beef patties, special sauce, lettuce, cheese, pickles, onions, and sesame-seed bun made it especially suitable for product-focused branding. The sandwich quickly became one of the company's defining menu symbols.
The Big Mac's identity was reinforced through advertising, packaging, and later international promotions. Its name also became a familiar shorthand for McDonald's itself, particularly when discussing the brand's global reach.
The Quarter Pounder, Filet-O-Fish, and Egg McMuffin are also major McDonald's products, but they do not answer this specific branding-history question. The important distinction is between a popular menu item and the product that became the focus of McDonald's early nationwide signature-item advertising.