"The Minstrel Boy" was an Earth song that Chief Miles O'Brien often used as his "happy thought" in dire situations. His one-time captain, Benjamin Maxwell, and Will Kayden were also fond of the song. (TNG: "The Wounded").
The minstrel boy to the war is gone
In the ranks of death you will find him
His father's sword he hath girded on
And his wild harp slung behind him
"Land of Song" said the warrior bard
"Tho' all the world betrays thee
One sword, at least, thy right shall guard
One faithful harp shall praise thee"
The minstrel fell, but the foeman's chain
Could not bring that proud soul under
The harp he lov'd ne'er spoke again
For he tore its cords asunder
And said "no chains shall sully thee,
Thou soul of love and bravery
Thy songs were made for the pure and free
They shall never sound in slavery"
In "The Wounded", the song is both sung by O'Brien and Maxwell and used as a thematic overture.
The tune of "The Minstrel Boy" is played in the soundtrack of the Star Trek: Deep Space Nine seventh season episode "What You Leave Behind". It can be heard playing during the scene where O'Brien takes one last look at his quarters and finds the figurine of William B. Travis.
The tune of "The Minstrel Boy" is also played in the soundtrack of the TNG episode "Hollow Pursuits". It can be heard playing during the scene where Lieutenant Reginald Barclay is seen leaving the Holodeck at the end of the episode.
The song was to have been included in DS9: "Whispers", where the Parada replicant of O'Brien would have sung it. The scene can be found in the shooting script. (Star Trek: Deep Space Nine Companion (p. ?))
"The Minstrel Boy" is believed to have been written by Irish poet Thomas Moore (1779-1852) to commemorate friends who had died in the 1798 Irish rebellion against British rule. The song has been used in many film and television productions including The Man Who Would be King (starring Michael Caine, Sean Connery, and Christopher Plummer) and Black Hawk Down (which starred Tom Hardy).