real MacKay

Etymology
Attested in 1856 as “A drappie o’ the real MacKay” (A drop of the real MacKay). Used as advertising slogan of G. MacKay & Co., Ltd., a whisky distiller.

Later attested 1883, Robert Louis Stevenson:
 * For society, there isna sae muckle, but there’s myself—the auld Johnson, ye ken—he’s the real Mackay…

Noun

 * 1)  The real McCoy, the genuine article, not an imitation.

Descendants

 * the real McCoy