Michael Joseph O'Rahilly, known as The O'Rahilly, was an Irish republican and nationalist. He was a founding member of the Irish Volunteers in 1913 and served as Director of Arms. Despite opposing the action, he took part in the Easter Rising in Dublin and was killed in a charge on a British machine gun post covering the retreat from the Dublin GPO during the fighting.

The Irish Volunteers, also known as the Irish Volunteer Force or the Irish Volunteer Army, was a paramilitary organisation established in 1913 by nationalists and republicans in Ireland. It was ostensibly formed in response to the formation of its Irish unionist/loyalist counterpart the Ulster Volunteers in 1912, and its declared primary aim was "to secure and maintain the rights and liberties common to the whole people of Ireland". Its ranks included members of the Conradh na Gaeilge, Ancient Order of Hibernians, Sinn Féin and the Irish Republican Brotherhood. Increasing rapidly to a strength of nearly 200,000 by mid-1914, it split in September of that year over John Redmond's support for the British war effort during World War I, with the smaller group opposed to Redmond's decision retaining the name "Irish Volunteers".