The Real McCoy

"The real McCoy" is an idiom and metaphor used in much of the English-speaking world to mean "the real thing" or "the genuine article", e.g., "he's the real McCoy". It is a corruption of the Scots "The real MacKay", first recorded in 1856 as: "A drappie o’ the real MacKay," (A drop of the real MacKay), and this is widely accepted as the origin.