The McDonald's mascot known for stealing hamburgers was the Hamburglar.
The Hamburglar first appeared in national McDonald's advertising in 1971. Early versions of the character were small and mischievous, while later redesigns gave him a more recognizable childlike appearance with a black-and-white outfit and red cape.
His role was simple: he wanted hamburgers, especially McDonald's hamburgers, and often tried to take them. That playful premise made him a recurring comic foil in McDonaldland commercials rather than a realistic villain.
The Hamburglar was part of a larger character system that included Ronald McDonald, Grimace, and Mayor McCheese. He is sometimes mistaken for a general nickname for McDonald's customers or a one-off advertising figure, but he was an established branded mascot.