John O ' Mahony John Francis O ' Mahony ( 1816 – 7 February 1877 ) was a Gaelic scholar and the founding member of the Fenian Brotherhood in the United States , sister organisation to the Irish Republican Brotherhood . Early life . He was born in 1816 in Kilbeheny , County Limerick , Ireland . His father and uncle had been members of the United Irishmen , and had taken part in the Irish Rebellion of 1798 . On the death of an elder brother , he inherited a property which yielded £300 per annum . He ignored a ban by the Roman Catholic Church , and entered Trinity College , Dublin , where he studied Sanskrit , Hebrew and Irish . He became an accomplished Gaelic scholar , and later taught Greek and Latin , and contributed articles to Irish and French journals . He left Trinity without getting a degree . Irish Politics . In 1843 , he joined Daniel O ' Connell ' s movement for the Repeal of the Union Act of 1800 , but quickly became dissatisfied with the lack of progress and joined " Young Ireland er " movement which Smith O ' Brien led and took part in the failed Young Irelander Rebellion of 1848 . Emigration . His participation in the rebellion obligated him to leave Ireland , and he settled for a time in Paris , where he lived in great poverty . In 1854 , he joined John Mitchel in New York City , and took part in the Emigrant Aid Association , the Emmet Monument Association , and other Irish organisations . It has been said that the Fenian Society originated in America and was transplanted to Ireland ; but , as a matter of fact the plans for both the Irish and American organisations were drawn in Paris by a small group of the Irish revolutionary exiles in 1848 . " History of Ireland " . In 1857 , he published " History of Ireland , by Geoffrey Keating , D . D . , translated from the Original Gaelic , and Copiously Annotated " ( New York , 1857 ) . Dr . Todd , in his preface to the " Wars of the Gaedhill with the Gaell " , says : " His translation of Keating is a great improvement upon the ignorant and dishonest one published by Mr . Dermod O ' Connor more than a century ago , but has been taken from a very imperfect text , and has evidently been executed , as he himself confesses , in great haste . " O ' Mahony ' s notes are copied from O ' Donovan ' s " Four Masters " , and it was on this ground that Hodges & Smith procured an injunction against the sale of the book in the United Kingdom . The mental strain to which O ' Mahony was subjected in the preparation of this work , which brought him no pecuniary gain , affected his reason , and he was removed by his friends for a short time to a lunatic asylum . Fenian Brotherhood . In 1860 , O ' Mahony organised the Fenian Brotherhood , also known as the Irish Republican Brotherhood . The object of the association was to secure the freedom of Ireland . The name was probably derived from O ' Mahony ' s Gaelic studies , the Fenians having been a military body in pagan Ireland , celebrated in the songs of Ossian . The early portion of Keating ' s " History " is occupied with the exploits of the ancient Fenians . The organisation of the new society was completed at conventions that were held in Chicago in 1864 , and in Cincinnati in January 1865 . Civil War . At the time of the Cincinnati convention , O ' Mahony held the rank of colonel of the 69th Regiment of New York State Militia , recruited mainly from the ranks of the Brotherhood , which had also furnished a large proportion of Meagher ' s Irish Brigade , the Corcoran Legion , and Irish regiments engaged in the US Civil War . The rapid growth in membership of the Fenian Brotherhood rendered it impossible for O ' Mahony to retain the colonelcy of the 69th regiment , which he had held for some time , and resigning he gave all his attention to the spread of Fenianism . Fenian growth . The close of the civil war in the spring of 1865 gave a great impetus to the Fenians , owing to the number of Irish - American soldiers that were disbanded and anxious to see service elsewhere . Money poured into the Fenian exchequer ; probably $ 500 , 000 was subscribed between 1860 and 1867 . Many differences occurred between O ' Mahony and James Stephens and the Central Council relative to the policy to be pursued for the attainment of their object , but O ' Mahony remained president of the organisation for several years . He did not take any part personally in the attempted insurrection in Ireland or in the raids on Canada , although his advice counted for much in these enterprises . Later years . He devoted the last years of his life to literary pursuits , but suffered from ill health , and he had a hard struggle to secure the bare means for subsistence . However visionary may have been his objects , he was honest , and although thousands had passed through his hands , he was often at a loss for a dollar . When his poverty was discovered , he declined to receive assistance in any shape . He died in New York City in 1877 and was interred in Glasnevin Cemetery in Dublin .