Grimace originally had four arms and was associated with stealing milkshakes.
When Grimace was introduced in 1971, the character was portrayed as a large, unsettling figure with four arms. The early design supported a comic advertising premise in which Grimace could take multiple drinks at once, linking the character to McDonald's shakes.
McDonald's later redesigned Grimace into the soft, purple, friendly character most audiences recognize. The simplified version had two arms and a less threatening appearance, making Grimace better suited to children's advertising and group appearances with Ronald McDonald.
People often remember only the later design and miss this unusual early history. Grimace was not originally a generic purple mascot, and the character's role was not always the same. The four-armed version is a branding detail from the character's first period, while later campaigns emphasized friendship and playful participation rather than theft.