McDonald's 1960s logo mascot before the Golden Arches became dominant was Speedee.
Speedee originated in 1948, when the McDonald brothers promoted their Speedee Service System. The character wore a chef's outfit and had a hamburger-shaped head, visually connecting fast service with the food being sold. His name came from the restaurant system's emphasis on quick, repeatable preparation.
McDonald's used Speedee in branding before the company adopted the Golden Arches as its principal national symbol. The transition reflected the chain's changing needs: a mascot communicated service and food, while the arches could function as a simple architectural and corporate sign visible from a distance.
This question is sometimes confused with Ronald McDonald, who became the company's best-known character after appearing in advertising beginning in the early 1960s. Speedee was the earlier mascot. Mayor McCheese and Grimace belonged to the later McDonaldland advertising world, not the original Speedee identity.