Eoghan Rua Ó Néill, anglicised as Owen Roe O'Neill (c. 1590–1649) ("Red Owen"), was a seventeenth century soldier and one of the most famous of the O'Neill family of Ulster.
But jealousy between the kinsmen was complicated by differences between Owen Roe and the Catholic Confederation which met at Kilkenny in October 1642. Owen Roe professed to be acting in the interest of Charles I; but his real aim was the complete Independence of Ireland as a Roman Catholic country, while the Old English Catholics represented by the council desired to secure religious liberty and an Irish constitution under the crown of England. More conceretely, O'Neill wanted the Plantation of Ulster overturned and the recovery of the O'Neill clan's ancestral lands. Moreover, he was unhappy that the majority of Confederate military resources were directed to Thomas Preston's Leinster Army. Preston was also a Spanish veteran but he and O'Neill had an intense personal dislike of each other.
Although Owen Roe O'Neill was a competent general, he was outnumbered by the Scottish Covenanter army that had landed in Ulster in 1642. Following a reverse at Clones, O'Neill had to abandon central Ulster and was followed by thousands of refugees, fleeing the retribution of the Scottish soldiers for some atrocities against Protestants in the rebellion of 1641. O'Neill complained that the devastation of Ulster made it look, "not only like a desert, but like hell, if hell could exist on earth". O'Neill did his best to stop the killings of Protestant civilians, for which he received the gratitude of many Protestant settlers. From 1642-46 a stalemate existed in Ulster, which O'Neill used to train and discipline his Ulster Army. This poorly supplied force nevertheless gained a very bad reputation for plundering and robbing friendly civilians around its quarters in northern Leinster and southern Ulster.
In 1646 O'Neill, furnished with supplies by the Papal Nuncio, Giovanni Battista Rinuccini, attacked the Scottish Covenanter army under Major-General Robert Monro, who had landed in Ireland in April 1642. On 5 June 1646 O'Neill utterly routed Monro at the Battle of Benburb, on the Blackwater killing or capturing up to 3000 Scots. However after being summoned to the south by Rinuccini, he failed to take advantage of the victory, and allowed Monro to remain unmolested at Carrickfergus.
So alienated was O'Neill by the terms of the peace the Confederates had made with Ormonde that he refused to join the Catholic/Royalist coalition and in 1648 his Ulster army fought with other Irish Catholic armies. He made overtures for alliance to Monck, who was in command of the parliamentarians in the north, to obtain supplies for his forces, and at one stage even tried to make a separate treaty with the English Parliament against the Royalists in Ireland. Failing to obtain any better terms from them, he turned once more to Ormonde and the Catholic confederates, with whom he prepared to co-operate more earnestly when Cromwell's arrival in Ireland in August 1649 brought the Catholic party face to face with serious danger.
The Catholic nobles and gentry met in Ulster in March to appoint a commander to succeed Owen Roe O'Neill, and their choice was Heber MacMahon, Roman Catholic Bishop of Clogher, the chief organizer of the recent Clonmacnoise meeting. O'Neill's Ulster army was unable to prevent the Cromwellian conquest of Ireland, despite a successful defence of Clonmel by Owen Roe's nephew Hugh Dubh O'Neill and was destroyed at the Battle of Scarrifholis in Donegal in 1650. Its remnants continued guerrilla warfare until 1653, when they surrendered at Cloughoughter in county Cavan. Most of the survivors were transported to serve in the Spanish Army.
In the nineteenth century, O'Neill was celebrated by the Irish nationalist revolutionaries, the Young Irelanders, who saw O'Neill as an Irish patriot. Thomas Davis wrote a famous song about O'Neill, titled "The Lament for Owen Roe". which was popularised in their newspaper, The Nation.