Don't know if anyone else had reason to use Google search today, but they often recognize the birthday of historical figures, and today they honor Elijah McCoy, African-American inventor of an early mechanical locomotive lubricator that was considered so good that railroad mechanics insisted on getting "The real McCoy". Hence the saying...

One of about four or five etymologies/stories about how the saying supposedly originated........

Seems like it's generally accepted that his name was the origin of the phrase. At least in as much as we can be sure of anything like that from over 100 years ago.

Any way cool info thanks.

Some years ago the Wright Museum of African-American History at Detroit asked if we had any information on what it was McCoy actually invented. At the time all I could do was foist them off on John H. White. Shortly thereafter I learned that McCoy's drawings and original patent model were the subject of a nice exhibit at the Henry Ford. Don't know if it's still on display.