Cormac MacBaron O'Neill

Sir Cormac MacBaron O'Neill (d.1613) was an Irish soldier and landowner of the Elizabethan and early Stuart eras. He was part of the O'Neill dynasty, one of the most prominent Gaelic family in Ireland.

O'Neill was the son of Matthew O'Neill, 1st Baron Dungannon, who was assassinated by his half-brother and rival Shane O'Neill in 1558. His 'middle name' was a Patronymic, denoting his father's title. O'Neill's older brother was Hugh O'Neill, Earl of Tyrone.

Despite their father's defeat to Shane, Cormac and Hugh were able to re-establish themselves in Ulster thanks to help from the government. When Hugh, having been recognised as Earl of Tyrone by the Crown, then launched a rebellion in 1594, Cormac joined forces with him. He took part in the Siege of Enniskillen and the Battle of the Ford of the Biscuits the same year. Following their defeat at the Battle of Kinsale, Cormac remained loyal to his brother when most of his other Gaelic Irish changed sides and made peace with the Crown. Following the Burning of Dungannon, in which Tyrone destroyed his own capital, they fought a guerrilla war, and Cormac was able to ambush a force led by Henry Docwra. Nonetheless his relationship with his brother became increasingly strained, despite the Treaty of Mellifont (1603) in which the Crown pardoned them and restored their lands.

When Hugh O'Neill fled Ireland in 1607, Cormac remained behind, riding to Dublin to inform the authorities of his brother's departure, and claiming he had no part in. Mistrusted by the authorities, however, Cormac was arrested and remained in prison for the remainder of his life, although he was never charged with any crime and government officials privately admitted he offered no threat, but should be kept locked up.

His son Conn MacCormac O'Neill (or Constantino O'Neill) was an officer in the Spanish Army. Like many Irish Catholics of the era he was a Wild Geese because the penal laws forbade him serving in the Irish Army. Conn was considered the heir to the Earl of Tyrone by some, but this was not formally recognized because of the Crown's earlier attainder.