General   (General discussion, talk about anything.)

The Real McCoy is an idiom or metaphor used in the English speaking world to mean ‘the real thing’ or ‘the genuine article’.

The phrase has been the subject of numerous false etymologies and attributions.

Here are a couple:-

The phrase has been associated with Elijah McCoy’s oil drip lubricator invention of 1872 which was used to oil train wheels.
The theory is that railroad engineers looking to avoid inferior copies would request it by name, inquiring if a lubricator was 'the real McCoy’.

OR

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 McKay," (A drop of the real MacKay), Messrs McKay of Edinburgh were makers of fine Whisy.
This appeared in a poem Devil's Halloween published in Glasgow and is widely accepted as the phrase's origin.