Denis O'Conor, O'Conor Don (; 1794–1847) of Clonalis, County Roscommon, was an Irish nobleman, and Member of Parliament (MP) in the British House of Commons. Early life and family He was born in May 1794 to Owen O'Conor, O'Conor Don and his wife Jane Moore daughter of Edward Moore of Mount Browne, Co. Dublin and Jane Reynolds. Denis was the eldest of four children. He had one brother Edward who became an agent for their father and then to Denis, and two sister Jane and Catherine. He was brought up in Belanagare in County Roscommon until his father moved the family to Clonalis on the death of his fourth cousin once removed, Alexander O'Conor, O'Conor Don in 1820 whom his father inherited the title of O'Conor Don. The O'Conors were prominent Catholic gentry who had been the traditional Kings of Connacht and counted among their ancestors two twelfth-century High-Kings of Ireland, Tairrdelbach Mor Ua Conchobair and Ruaidrí Ua Conchobair who was the last high king of Ireland. On his father's side, he was a nephew of Rev. Charles O'Conor and Matthew O'Conor. His father's first cousin was Thomas O'Conor and therefore Denis was a second cousin of Thomas's son Charles O'Conor of New York. His great-grandfather was the eminent antiquarian, writer and protagonist for catholic civil rights during the penal laws, Charles O'Conor of Belanagare. His maternal grandfather was a wealthy Catholic brewer in Dublin who was descended from Lewis O'More youngest brother of Rory O'More. His maternal grandmother was a daughter of Thomas Reynolds of Rathfarnham and Dundrum Castle. Thomas was a successful Silk manufacturer who descended from a cadet branch of Mac Raghnaill chiefs of Lough Scur in County Leitrim. Through this connection Denis's Mother was a first cousin of Thomas Reynolds. He was educated at St Edmund's College, Ware, Trinity College, University of Dublin, Lincolns Inn and the King's Inn to train as a barrister and took the Grand Tour in the early 1820s. Carear In the 1820s he supported the pro-Catholic agitation in Roscommon led by his father, the O’Conor Don, later that decade and assisted in his return for the county, following the granting of emancipation, in 1830. He moved the resolution for repeal of the legislative Union with Britain at a county meeting, on 14 January 1831, and seconded one in favour of parliamentary reform at another, on the 16 April 1831. On the