The ice cream treat debuted in 1970, and since then, McDonald's says the shamrock shake has stirred up a "cult-like" following who crave its icy goodness when the St. Patrick's Day season is nigh.
What you might not know is that it had its own mascot back in the day, named Uncle O'Grimacey, who of course, spoke like a stereotypical green Irish monster and extolled the virtues of all things green, including the shake.
