The Real McCoy Elijah McCoy inventions

The term "the real McCoy" comes from the automatic engine lubricator that Elijah McCoy invented (1843-1929) to continuously oil train & ship engines, which was immediately used by railroad & shipping lines. 

Imitations soon popped up but did not work as well as Elijahs' machine and that led many would-be buyers to ask "is this the real McCoy". Eventually the phrase was coined as a way to ask whether an item was authentic or not.