Danny Boy (Oh Danny Boy) is in fact one of many lyrics set to the folk
tune Londonderry Air. The origins of Londonderry Air are unknown, the
lyrics of Danny Boy however were written by the English lawyer,
Frederic Edward Weatherly (1848-1929). It appears that he originally
wrote a tune for his lyrics of Danny Boy, but the tune was not a
success. Some records indicate that Weatherly's American sister-in-law sent
him the tune of Londonderry Air, and Weatherly immediately realised
that it fit perfectly to his lyrics of Danny Boy. The tune is often
considered as Irish, even though Weatherly was English and Danny Boy is
popular around the entire English-speaking world. Weatherly’s won
biography entitled Piano ad Gowns (1926) shed more light on the
creation of Danny Boy:
In 1912 a sister-in-law in America sent me "The Londonderry Air". I had
never heard the melody or even heard of it. By some strange oversight
Moore had never put words to it, and at the time I received the MS. I
did not know that anyone else had done so. It so happened that I had
written in March of 1910 a song called "Danny Boy," and re-written it
in 1911. By lucky chance it only required a few alterations to make it
fit that beautiful melody. After my song had been accepted by a
publisher I got to know that Alfred Percival Graves had written two
sets of words to the same melody, "Emer's Farewell" and "Erin's
Apple-blossom," and I wrote to tell him what I had done. He took up a
strange attitude and said that there was no reason why I should not
write a new set of words to the "Minstrel Boy," but he did not suppose
I should do so! The answer of course is that Moore's words, "The
Minstrel Boy" are so "perfect a fit" to the melody that I certainly
should not try to compete with Moore. But beautiful as Grave's words
are, they do not to my fancy suit the Londonderry air. They seem to
have none of the human interest which the melody demands. I am afraid
my old friend Graves did not take my explanation in the spirit which I
hoped from the author of those splendid words, "Father o' Flynn."
However, "Danny Boy" is accepted as an accomplished fact and is sung
all over the world by Sinn Feiners and Ulstermen alike, by English as
well as Irish, in America as well as in the homeland, and I am certain
"Father o' Flynn" is equally popular, as it deserves to be, and its
author need have no fear that I shall be so foolish as to write a new
version of that song. (from Piano and Gowns, pp 277-279).
Danny Boy has been recorded by many artists, and featured in many
movies, most prominently in the 1990 motion picture Memphis Belle, where
a crooning Harry Connick Jr. gives the melody a very Jazzy inflection. It was also featured on The Danny Thomas TV show