The O'Rahilly was born Michael Joseph O'Rahilly (Irish: Mícheál Seosamh Ó Rathaille), (22 April 1875 - 29 April 1916). He was a Irish nationalist and took part in the Rising.
The O'Rahilly was part of the Volunteers that did not want to be part of an armed uprising. He was also left out of the planning for the Rising. However, after it started, he felt he needed to be part of the fray.
During the Rising, he led a force out of the GPO to locate a route to Williams & Woods, a factroy on Great Britian Street (renamed Parnell Street). He and his force met with machine-gun fire from the British force on Great Britian and Monroe Street. He was severely wounded, but ran across Sackville Street to get shelter from the machine-gun; however, he met with more machine-gun fire.
In Gaelic tradition, chief of clans were called by their clan name preceded by the determinate article, for example Robert The Bruce. O'Rahilly's calling himself "The O'Rahilly" was purely his own idea, and not a general recognition that he was the head of the O'Rahilly (or O'Reilly) clan. In 1938, the poet William Butler Yeats defended The O'Rahilly on this point in a well-known poem, which begins:
"Sing of the O'Rahilly,
Do not deny his right;
Sing a 'the' before his name;
Allow that he, despite
All those learned historians,
Established it for good;
He wrote out that word himself,
He christened himself with blood.
How goes the weather?"