Traditional

"Danny Boy" was written by the English lawyer and lyricist Frederick Weatherly in 1910. Although the lyrics were originally written for a different tune, Weatherly's sister modified them, in 1913, to fit "Londonderry Air" (Irish diaspora anthem : irish emigrants and their descendants in countries such as the United Kingdom, the United States, Canada, Australia, Argentina, New Zealand, Mexico, South Africa, Brazil and states of the Caribbean and continental Europe. The diaspora, maximally interpreted, contains over 80 million people, which is over eleven times the population of the island of Ireland itself).
"Danny Boy" was intended as a message from a woman to a man, and Weatherly provided the alternative "Eily dear" for male singers in his 1918 authorised lyrics. However, the song is actually sung by men as much as, or possibly more than, women. The song has been interpreted by some listeners as a message from a parent to a son going off to war.
The song is widely considered an Irish anthem, although Weatherly was an Englishman. (from Wikipedia).