The Real McCoy

:The Real McCoy was also a film starring Kim Basinger.

Origins

Michael Quinion of "World Wide Words" summarises the half dozen or so theories on the origin of this phrase:

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• Elijah McCoy, inventor of a lubrication system for steam engines.
• The McCoy family of an infamous family feud between the Hatfields and the McCoys on the West Virginia-Kentucky border in the late nineteenth century.
• A famous cattle baron by the name of McCoy (Alistair Cooke's theory).
• Bill McCoy, a rum-runner during the prohibition era.
• A reference to pure heroin imported from Macao.
• A boxer, Norman Selby, known as Kid McCoy, welterweight champion from 1898-1900. There are apocryphal tales to the effect that he had many imitators and had to adopt the term to distinguish himself.
• "The Real MacKay", a phrase that was said to appear first in 1856 as "A drappie o? the real MacKay", by the Scottish National Dictionary; the same work says that the phrase was later adopted as a slogan to promote MacKay's whisky. The Oxford English Dictionary quotes Robert Louis Stevenson from 1883 in a letter saying "He's the real Mackay".

McQuinion notes that many authorities favor the Kid McCoy story, but he personally finds the MacKay story more convincing because of the concrete evidence which generally predates the references supporting other stories.

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