O'NEILL, FAMILY. — Famous Irish family, descended from Niall, king of Ireland in the 5th century. To it belonged Muircheartach Mac Neill, who was perhaps the first king of Ireland to convert to Christianity in the 6th century.
Particular renown was acquired by HUGH O. (ca. 1540–1616), who, taking advantage of the misgovernment of the viceroys sent to the island during the reign of Elizabeth, led various insurrections, became a champion of freedom of conscience, and rallied the Catholics under his banner. Having obtained the support of Spain and the Holy See, he succeeded in conquering almost the entire island. In 1599 Clemente VII urged him, by a brief, to persevere in the defense of the Catholic faith and sent him a phoenix feather, a gift which O'N. interpreted as a recognition of his sovereignty over Ireland. From then on, the fortunes of war abandoned him. Having submitted to the Crown, he nevertheless no longer felt secure and,
fearing that he would be arrested, left the island in 1607 to settle in Rome, where he was received by Paolo V and where he died. The son of a younger brother of Hugh was EUGENIO O'N. (ca. 1590–1649), who, after having served Spain, returned to Ireland and became general of the army that Carlo I, engaged in the struggle against Parliament, was organizing on the island. He set himself the goal of Ireland’s complete independence and for this reason found himself in conflict with the Catholic Council, which was not unwilling to recognize, subject to guarantees of the rights of Catholics, the sovereignty of the king of England over the island. Other notable members of the family were DANIELE (ca. 1612–64), who on Eugenio’s death assumed command of the Irish forces, and GIOVANNI (1740–98), a member of the Irish Parliament and supporter of Catholic emancipation.