real mccoy, the

real McCoy, the

Also, the McCoy. The genuine thing, as in That painting's not a reproductionit's the real McCoy. This idiom has a disputed origin, but the most likely source is its use to distinguish welterweight champion "Kid McCoy," the name used by Norman Selby (1873-1940), from other boxers using his name to capitalize on his popularity. [c. 1900]