Who is John Barleycorn or to what does the name refer?
The references in The Big Book, The 12x12 and AA Comes of Age
were likely made in loose regard to the 1913 autobiographical novel
by the extremely popular American author Jack London that chronicled his struggles with alcoholism.
The novel's title "John Barleycorn" was taken from the British folksong of the same name. In the song John Barleycorn represents the vital barley grain crop and the beer and/or whiskey made from it.
In the song, John Barleycorn suffers pain, humiliation and death, in ways which are said to represent the growth, cutting and distilling of barley.
Around the time of the writing of much of A.A.'s literature "John Barleycorn" had come to be used as a euphemism for alcoholism or alcohol.
There are many different versions of the song and the content can vary considerably but generally have to do with themes of growth, suffering, death, alcohol, revenge... and barley.
An informative article on the subject can be found at http://en.wikipedia.org/wiki/John_Barleycorn