O'NEILL, FAMILY. - A celebrated Irish family descending from Niall, king of Ireland in the 5th century. Among its members was Muircheartach Mac Neill, who may have been the first Irish king to convert to Christianity in the 6th century.
Particular renown was achieved by HUGH O. (c. 1540–1616), who, taking advantage of the misrule of the viceroys sent to the island during the reign of Elizabeth, led several uprisings, championed freedom of conscience, and gathered Catholics under his banner. Having secured the support of Spain and the Holy See, he succeeded in conquering nearly the entire island. In 1599, Clement VII exhorted him in a brief to persevere in the defense of the Catholic faith and sent him a phoenix feather, a gift which O'N. interpreted as recognition of his sovereignty over Ireland. From that point onward, his military fortunes declined. Though he submitted to the crown, he did not feel secure and, fearing arrest, left the island in 1607 to settle in Rome, where he was received by Paul V and died there.
A nephew of Hugh was EUGENE O'N. (c. 1590–1649), who, after serving Spain, returned to Ireland and became general of the army that Charles I was raising on the island in his struggle against Parliament. He aimed at complete Irish independence and thus came into conflict with the Catholic Council, which was not averse to recognizing, with guarantees for Catholic rights, the sovereignty of the king of England over the island.
Other notable members of the family included DANIEL (c. 1612–64), who, upon Eugene’s death, took command of the Irish forces, and JOHN (1740–98), a member of the Irish Parliament and advocate of Catholic emancipation.