Speedee was McDonald's hamburger-headed mascot before Ronald McDonald.
Speedee was introduced in connection with the Speedee Service System, the streamlined operating method created by Richard and Maurice McDonald in 1948. The character represented quick service and was shown as a smiling figure with a hamburger-shaped head.
The mascot's name reflected the restaurant's emphasis on speed. It appeared in early McDonald's branding and signage before Ronald McDonald became the central advertising character in the early 1960s.
Speedee is often confused with the Hamburglar because both belonged to McDonald's character history. They served different roles: Speedee was the early service-system mascot, while the Hamburglar was a later McDonaldland character associated with stealing hamburgers. This question concerns the pre-Ronald mascot, not the later character cast.