Which advertising character became McDonald's first national mascot in the United States?

Ronald McDonald became McDonald's first national mascot in the United States.

McDonald's introduced Ronald McDonald in 1963 as a clown character designed to appeal to children. The character first appeared in advertising in the Washington, D.C., area before being adopted for national promotion.

Ronald's costume incorporated recognizable McDonald's imagery, including a meal-box-style outfit and the restaurant's colors. His arrival helped transform McDonald's branding from a restaurant-centered identity into a character-led family entertainment world.

Grimace, the Hamburglar, and Mayor McCheese became prominent McDonaldland characters later. The earlier Speedee mascot also appeared in McDonald's history, but Ronald McDonald is the character associated with the company's first major national mascot campaign.