The phrase "The real McCoy" may be a corruption of the Scots "The real MacKay", first recorded in 1856 as: "A drappie o' the real MacKay",. This appeared in a poem Deil's Hallowe'en published in Glasgow and is widely accepted as the phrase's origin. A letter written by the Scottish author Robert Louis Stevenson in 1883 contains the phrase, “He’s the real Mackay”. In 1881, the expression was used in James S. Bond's The Rise and Fall of the 'Union Club'; Or, Boy Life in Canada. A character says, "By jingo! yes; so it will be. It's the 'real McCoy,' as Jim Hicks says. Nobody but a devil can find us there." The expression has also been associated with Elijah McCoy's oil-drip cup invention. One theory is that railroad engineers looking to avoid inferior copies would request it by name, inquiring if a locomotive was fitted with 'the real McCoy system". This possible origin is mentioned in Elijah McCoy's biography at the National Inventors Hall of Fame. The original appearance of this claim in print can be traced to an advertisement which appeared in the December 1966 issue of Ebony. The ad, for Old Taylor Bourbon whiskey, ends with the tag line: "...but the most famous legacy McCoy left his country was his name." In the 1996 documentary The Line King, caricaturistAl Hirschfeld attributed the phrase to his friend 1930s pioneer radio host George Brainwood McCoy. McCoy proved he could live off the land without paying for food or rent. During the 1939 World's Fair he ate free food from the exhibitions, slept complimentary at the Royal Scot, shaved using the new electric shavers at the display exhibits, and earned spending money by selling his story to Life Magazine. During the second World War, McCoy could be heard broadcasting his radio show in 1944 Rome, where he would sign off saying: "This is Sergeant George McCoy folding his microphone and silently stealing away." Alternative attributions include:
A dispute between two branches of the Scots Clan Mackay over who was rightful leader. Lord Reay headed one branch and he came to be known as the Reay Mackay which migrated to 'the real McCoy'. See Huistean Du Mackay, 13th of Strathnaver for information about the dispute.
Joseph McCoy was mayor of Abilene, Kansas and styled himself 'the real McCoy'.
In the United States, the phrase became associated with boxer Kid McCoy. Quinion notes that "It looks very much – without being able to say for sure – as though the term was originally the real Mackay, but became converted to the real McCoy in the U.S., either under the influence of Kid McCoy, or for some other reason."
