Gearóid O'Sullivan (28 January 1891 – 25 March 1948) was an Irish teacher, Irish language scholar, army officer, barrister and Sinn Féin and Fine Gael politician.^[1]

Jeremiah O'Sullivan was born in Coolnagurrane near Skibbereen, County Cork,^[2] he was the fourth son of Michael and Margaret O'Sullivan and given the name of Jeremiah - but known throughout his lifetime as Gearóid. His father, a native of Lough Ine, and his mother, née McCarthy, a Coolnagurrane native, were members of West Cork farming families.^[3] Early in his education at the local national primary school, his intellectual capacity and promise of greater things was often remarked upon. Despite his young age, he was selected school monitor – to monitor the progression of fellow students as well as the teaching capabilities of the teacher.^{[citation needed]}

He next studied at Daniel Duggan's Intermediate and University School in Skibbereen; at about this time, he was to meet several individuals who would draw him further into the Irish nationalist movement and deepen his appreciation of Irish language and culture.^{[citation needed]} These included James Duggan, a local Sinn Féin activist and acquaintance of Gearóid's cousin Michael Collins. The two shared a grandmother on the McCarthy side of their respective families. Duggan encouraged Gearóid to join the Gaelic League, which he did at the age of ten in October 1900.^[3] Notably, Gearóid's father, Michael O'Sullivan, chose to complete the family's 1911 Census form in Irish.^{[citation needed]}

In 1909, O'Sullivan started at St Patrick's College of Education, in Drumcondra, Dublin, to train for a career in teaching. While not quite 19, he had already completed the second arts examination of the Royal University of Ireland. He took up teaching in 1911. A first posting was to Kildorrey, Cork in 1912, but soon transferred back to Dublin to teach at St Peter's National School, Phibsborough. He joined the Keating branch of the Gaelic League, quickly assuming a leadership role within the organisation and tirelessly travelling to teach Irish to League members while also studying for H Dip Ed at the National University and drilling with the Irish Volunteers. At 25 Parnell Square, the drill hall, he established the "faine" proficiency test for recruiting.^[4] It was also here that he became re-acquainted with Michael Collins, who joined the League in 1916 upon his return to Ireland from London, where he'd held a Postal Service position.^[3]

In November 1913, O Sullivan was appointed to F Company, 1st battalion, said to be the best of Dublin Brigade.^[5] In addition to patrolling with the Irish Volunteers, O'Sullivan had the distinction shared by a small proportion of later "original IRA" members of being a member of the Irish Republican Brotherhood (IRB), which traces its roots to earlier revolutionary movements of the mid-Nineteenth Century. He also notably raised the Irish Flag over the General Post Office (GPO) in Dublin^[2] as fighting raged around the GPO and the streets of Dublin during the 1916 Easter Rising.

O'Sullivan, then 25, was the youngest IRB officer fighting in the GPO.^[6] He had been personally chosen by rebellion leader Seán Mac Diarmada to serve as his aide-de-camp. The additional honour of raising the Irish flag was given to him by another of the rebellion's leaders, Patrick Pearse. He married Maud Kiernan, sister of Kitty Kiernan,^[2] daughter of Peter and Bridget Kiernan of the Greville Arms Hotel, Granard, County Longford, with whom he had three daughters and a son. His wife died at age 40 and he remarried, to Mary ("Mae") Brennan of Belfast.^[3]

O'Sullivan died on 25 March 1948,^[1] aged 56, and received a state funeral on the following Easter Monday – exactly 32 years after the Easter Rising.^[2] Thousands of people lined the streets of Dublin to watch as a horse-drawn carriage carried his coffin – draped in the same Tricolor that had covered Collins' coffin a quarter-century earlier – past the GPO and other landmarks to his final resting place at Glasnevin Cemetery. He died leaving a second wife, Mary Brennan of Belfast, and his four children.

In O'Sullivan's obituary appearing in the Irish Independent, an individual ^[who?] describing himself as "a colleague" wrote of O'Sullivan's contributions to Ireland following 1916:

"When the jails and prison camps opened Gearoid came back to resume the struggle. At a critical moment and at the instance of Michael Collins, he was summoned to an honourable, if highly dangerous, post – to replace Collins as Adjutant-General of the Volunteers. In the stern years that followed there was no braver heart or cooler head in the councils of the nation's army. From his dingy office, within a stone's throw of Dublin Castle, surrounded by excursions and alarms, meeting places where plans for action were settled, and thence to an uneasy rest."