Uncle O'Grimacey was a McDonald's advertising character associated with the Shamrock Shake.
The character appeared as the uncle of Grimace and was used to promote the seasonal mint-flavored shake around St. Patrick's Day. His green appearance and Irish-themed presentation reinforced the product's limited-time association with the holiday.
The Shamrock Shake was introduced in 1970 and became a recurring seasonal item. Its availability has varied by market and year, but the product has remained one of McDonald's best-known holiday-linked promotions.
Uncle O'Grimacey is sometimes confused with Grimace, who became a broader McDonaldland mascot. Grimace was a general character, while Uncle O'Grimacey was specifically tied to the Shamrock Shake campaign.