the genuine thing or person as promised, stated, or implied (usually preceded by the or the real):
Those other paintings are copies, but this one is the McCoy.
1880-85; also Mackay, McKie, the clear McCoy (of liquor); of uncertain origin; hypothesized identifications with Mackay, a Scottish clan, and Kid McCoy, nickname of U.S. boxer Norman Selby (1873-1940), are unsubstantiated
as in the real McCoy, 1922, from Scot. the real Mackay (1883), of uncertain origin, though there are many candidates, including whiskey distilled by A. and M. Mackay of Glasgow (the phrase the real McCoy became popular during Prohibition to describe liquor); Charles S. "Kid" McCoy (1872-1940), former welterweight boxing champ; and a claimant for chief of the northern branch of the clan Mackay.