Hugh O'Neill was an Irish Gaelic lord, Earl of Tyrone and was later created The Ó Néill Mór, Chief of the Name. O'Neill's career was played out against the background of the Tudor conquest of Ireland, and he is best known for leading a coalition of Irish clans during the Nine Years' War, the strongest threat to the House of Tudor in Ireland since the uprising of Silken Thomas against King Henry VIII.

The Tudor conquest of Ireland took place during the 16th century under the Tudor dynasty, which ruled the Kingdom of England. The Anglo-Normans had conquered swathes of Ireland in the late 12th century, bringing it under English rule. In the 14th century, the effective area of English rule shrank markedly, and from then most of Ireland was held by native Gaelic chiefdoms. Following a failed rebellion by the Earl of Kildare in the 1530s, the English Crown set about restoring its authority. Henry VIII of England was made "King of Ireland" by the Crown of Ireland Act 1542. The conquest involved assimilating the Gaelic nobility by way of "surrender and regrant"; the confiscation and colonization ('plantation') of lands with settlers from Britain; imposing English law and language; banning Catholicism, dissolving the monasteries and making Anglican Protestantism the state religion.