Also, the McCoy. The genuine thing, as in That painting's not a reproduction—it'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]

The best of its kind, the real thing: “That homemade pizza was the real McCoy.” The source of this expression is the story of a famous prizefighter named McCoy. He had so many imitators that no one was sure which was the real one.