Grimace was introduced by McDonald’s in 1971 as a purple character whose identity was initially unclear.
The earliest version of Grimace was designed as a large, somewhat mischievous character with multiple arms who was associated with stealing milkshakes. McDonald’s later simplified the design, removing the extra arms and shifting Grimace toward the friendly, clumsy personality recognized by most audiences. The character became part of the McDonaldland cast alongside Ronald McDonald and the Hamburglar.
Unlike a mascot built around one obvious food item, Grimace was memorable because of his shape, color, and unusual name. For many years McDonald’s advertising did not give a precise species or biological description, which led audiences to debate what he was supposed to be.
That ambiguity is why answers such as “purple monster” are descriptions rather than the canonical name. Grimace is also distinct from Birdie, a yellow character introduced later to promote breakfast, and from the Hamburglar, whose identity and costume were built around stealing hamburgers.