Owen Roe O'Neill (c.1585-1649), a member of the O'Neill dynasty of Ulster, was a veteran soldier who had spent most of his life serving as a mercenary in the Spanish Army. Following the Irish Rebellion of 1641 in which Catholics rose up to assert their rights while pledging their allegiance to Charles I, O'Neill returned to Ireland. During the ensuing Irish Confederate Wars he commanded the Ulster Army, mostly campaigning against the Scottish Covenanter Army whom he defeated at the Battle of Benburb. Following the execution of Charles I in 1649 and the declaration of the English Commonwealth, the Irish Confederates and the Covenanters united in a new alliance under his son Charles II. In the face of a potential landing by a large expedition of English troops, O'Neill quarreled with his rival Catholic commanders and refused to accept the Treaty. He instead began co-operation with local English troops under Sir Charles Coote, assisting them during the Siege of Derry.