Zorro, the name of the band is Hothouse Flowers, and Liam O Maonlai is the Irish singer in that band who is often credited with bringing the song to the attention of other Irish artists, rightly or wrongly.

I know of no one in the music community in Ireland who has ever claimed that the song was Irish. Rather, it is believed to be an American song, which evokes and appeals to a certain sort of Irish poetic sensibility. In other words, a lot of Irish singers have responded to it as a great song.