Grimace was introduced in 1971 as a milkshake-stealing villain in McDonaldland advertising.
The character originally appeared as a large purple figure with four arms and a mischievous role. His early advertising identity centered on taking milkshakes, making him an antagonist for Ronald McDonald and the other McDonaldland characters.
McDonald's later changed Grimace into the friendly, simple character widely recognized today. The redesign reduced his arms and softened his personality, turning him into a companion rather than a threat. That transformation is why older descriptions of Grimace can differ sharply from modern depictions.
Grimace is often confused with the Hamburglar because both began as troublemakers in McDonaldland commercials. The Hamburglar focused on stealing hamburgers, while Grimace's original specialty was milkshakes.