Grimace was originally created as a milkshake thief before becoming friendly.
When Grimace was introduced in 1971, the character had four arms and was described in advertising as a villain who stole milkshakes. This early version fit the comic troublemaker pattern used by McDonaldland characters, giving Ronald McDonald and others a character to oppose.
McDonald’s later redesigned Grimace as a large, soft, purple character with two arms and a much more gentle personality. The change made him better suited to the friendly, humorous image the company wanted for family advertising. His exact species was not consistently defined, which helped keep the character fantastical.
Modern audiences often know Grimace mainly as a cheerful companion associated with McDonald’s. That familiar image can obscure his original role, which was specifically tied to taking milkshakes rather than hamburgers.