Shane O'Neill (; 1530 – 2 June 1567) was an Irish chieftain of the O'Neill dynasty of Ulster in the mid-16th century. Shane O'Neill's career was marked by his ambition to be the O'Neill—sovereign of the dominant O'Neill family of Tír Eoghain. This brought him into conflict with competing branches of the O'Neill family and with the English government in Ireland, who recognised a rival claim. Shane's support was considered worth gaining by the English even during the lifetime of his father Conn O'Neill, 1st Earl of Tyrone (died 1559). But rejecting overtures from the 3rd Earl of Sussex, the lord deputy from 1556, Shane refused to help the English against the Scottish settlers on the coast of Antrim, allying himself for a short time instead with the MacDonnells, the most powerful of these settlers. Shane viewed the Scottish settlers as invaders, but decided to stay his hand against them with hopes of using them to strengthen his position with the English. However, tensions quickly boiled over and he declared war on the Scottish MacDonnell's defeating them at the Battle of Glentaisie despite the MacDonnells calling for reinforcements from Scotland. The Scottish MacDonnells would later assassinate Shane O'Neill and collect the bounty on his head.

Name The name "Shane" is an anglicisation of the Irish name "Séan" (John). Shane's name is given in the Annals of the Four Masters (at M1567.2) as "Sean mac Cuinn, mic Cuinn mic Enri, mic Eocchain" ("John son of Conn, son of Conn, son of Henry, son of Eoin"). Elsewhere in the Annals (e.g. at M1552.7) he is referred to as "Sean Donngaileach Ó Neill".O'Donovan (1851), p. 1525 This refers to the fact that as a youth he was fostered by his cousins, the O'Donnelly Clan, of which the Chief was Marshal of the O'Neill forces. This was rendered as anglicisations such as "Donnolloh" in contemporary manuscripts,For example, and as "John, or Shane Doulenagh O'Neil" in Abbé MacGeoghegan's 1758 History of Ireland. It would now be properly rendered as Donnellagh. After he assumed the leadership of the O'Neills, he was referred to simply as "Ó Néill" ("The O'Neill").

The nickname "Shane the Proud" (), which appears in nineteenth- and early-twentieth-century popular histories, was coined sometime after his death by English writers, and originally had the pejorative meaning of "arrogant", because they wished to portray him as vain, self-indulgent and ruthless, and thus undermine the legitimacy of his claim to the earldom of Tyrone. Holinshed's Chronicles of 1587, for instance, had a side-note, "The proud taunts of Shane O'neile", the text remarking that "when the commissioners were sent to intreat with him vpon sundrie points, they found him most arrogant & out of all good order, braieng out spéeches not méet nor séemelie." Later Irish writers, such as John Mitchel and P. J. O'Shea (Conán Maol) used the nickname with more positive connotations.

Early life Shane was born , to Conn Bacach O'Neill, chief of the O'Neills of Tyrone, and Sorcha O'Neill, daughter of Hugh Oge O'Neill, chief of the O'Neills of Clandeboye. Shane's mother died while he was very young and Shane, following Gaelic custom, was fostered by the O'Donnelly family, who raised him until adulthood. As the youngest of Conn's six sons, the fact that he was not sent to one of the great families for fostering suggests that he was not expected to achieve much status. He was briefly abducted in 1531 by a rival O'Neill family, but otherwise, nothing is known about his youth.

Feuding within the O'Neill lordship The English, since the late 1530s, had been expanding their control over Ireland, this century-long effort is known as the Tudor conquest of Ireland. To incorporate the native Irish lordships, they granted English titles to Irish lords—thus making Conn Bacach O'Neill, Shane's father, the first Earl of Tyrone. However, whereas in Gaelic custom the successor to a lordship was elected from his kinsmen in the system of Tanistry, the English insisted on succession by the first-born son or primogeniture. This created a conflict between Shane, who considered it his natural right to be head of his clan, and an "affiliated son" or adopteeMorgan, Hiram Tyrone's Rebellion (1993) pp. 86–7. The genealogy of the O'Neills that Hiram Morgan has prepared notes Matthew as "affiliated". of his father Conn Bacach, Matthew O'Neill or Fear Dorcha who was 'conveniently mistaken' as the offspring of Conn when he travelled to London in 1542 to be invested with the Earldom of Tyrone. Feardorcha had accompanied Conn's entourage as the Earl's eldest son Phelim Caoch O'Neill had been killed by his enemy Gillespic MacDonnellDonald M. Schlegel, "The MacDonnells of Tyrone and Armagh: A Genealogical Study", Seanchas Ardmhacha, vol. 10, no. 1 (1980/1981), p. 205 during a raid in Ulster shortly before Conn's inauguration visit. Gillespic MacDonnell's family were noted as committed adherents of Feardorcha and his descendants.

During his trip to the English court to receive the title of earl of Tyrone, Shane's father Conn Bacach, who had just lost his eldest son and was in open conflict with his surviving sons, was accompanied by the fosterling Mathew (known as Feardorcha in Irish), a youth who, until he was sixteen had been acknowledged as the son of a Dundalk blacksmith.Richard Bagwell, Ireland Under the Tudors, (3 Vols) London, vol ii, pp. 2–4. Feardorcha's mother Alison Kelly was Conn Bacach's lover.

When Conn was created earl of Tyrone, Mathew was declared to be Conn's heir in English law, disinheriting all of Conn's surviving sons, including Shane. Under English law, Mathew, titled Baron of Dungannon from Conn's principal house in Tyrone, was intended to succeed him as 2nd Earl of Tyrone. However, Mathew was ambushed and killed by Shane's foster brothers, the O'Donnelly, in 1558, some months before the death of Conn Bacach, and the claim to the earldom passed to Brian, Mathew's eldest son, who was later killed in 1562 in a skirmish with Turlough Luineach.

The claim to the earldom now passed to Mathew's next son Hugh O'Neill who had been removed to England by Sir Henry Sidney in 1559 and was brought up there while Shane established his supremacy in Ulster; some sources say it was to the Pale that he was removed.

Becoming the O'Neill Shane was inaugurated as the O'Neill. In English law, this was an illegal usurpation of the rulership of Ulster. But according to Brehon law succession (tanistry), Shane had every claim to be chief of the name. The case for Mathew's disqualifying status under both English and Irish law, as an affiliated member of the family rather than as an actual son of Conn Bacach,Sean Ghall, "An Historical Note on Shane O'Neill", The Catholic Bulletin, vol XIII, April–May 1923, pp. 311–314. was carefully stated by Shane when he made his own claim to the title of Earl of Tyrone both before and during his visit to Queen Elizabeth in 1562,JS Brewer and W Bullen, (eds), Calendar of the Carew Manuscripts Preserved in the Archepiscopal Library at Lambeth, 1515–1624, (6 vols), London, vol. i, pp. 304–8; Ciarán Brady "The Government of Ireland, circa 1540–1583' PhD Trinity college, Dublin, 1981, pp. 153–4, 180–5. and restated in some detail by the English authorities when Hugh O'Neill was outlawed during the Nine Years' War.

Relationship with the English Although the O'Neill had allied himself against the English with the Scottish MacDonnell clan, who had settled in Antrim, Queen Elizabeth I, on succeeding to the English throne in 1558, was inclined to come to terms with the O'Neill, who after his father's death functioned as de facto head of the dynasty. She accordingly agreed to recognise his claims to the lordship, throwing over Brian O'Neill, son of the assassinated Feardorcha, Baron of Dungannon, if the O'Neill would submit to her authority and that of her deputy. O'Neill refused to put himself in the power of the Earl of Sussex, Thomas Radclyffe, without a guarantee for his safety; and so Elizabeth decided to establish Brian in his place.

An attempt by Sussex to increase the enmity of the O'Donnells against the O'Neill was frustrated by his seizure of Calvagh O'Donnell in a monastery. Elizabeth, whose prudence and parsimony were averse to so formidable an undertaking as the complete subjugation of the powerful O'Neill, desired peace with him at almost any price. Elizabeth's faith in Sussex's aggressive strategy diminished when the repeated annual devastations of O'Neill's territory by the Lord Deputy with sizeable and expensive armies failed to bring him to submission.

The O'Neill destroyed the greater part of Sussex's invasion army at the Battle of the Red Sagums, 18 July 1561, while Sussex was deep in O'Neill-controlled territory garrisoning Armagh with a small body of men. Afterwards, Elizabeth sent the Earl of Kildare to arrange terms with the O'Neill, who was demanding a complete withdrawal of the English from his territory. Unable to succeed against O'Neill in battle, Sussex tried in 1561 to assassinate him using poisoned wine. The O'Neill now called the lord deputy to account for his unnatural enmity, as displayed in this most recent of many attempts on his life.

Elizabeth consented to treat, and hostilities ceased on terms that gave the O'Neill practically all his demands. The O'Neill offered some concessions, most significantly consenting to present himself before Elizabeth in London to argue his case against Sussex and the Baron of Dungannon in person. The O'Neill requested the hand of Sussex's half-sister Lady Frances Radclyffe in marriage as an earnest of future friendship. Accompanied by the Earls of Ormonde and Kildare as surety for his safety, the O'Neill reached London on 4 January 1562. William Camden describes the wonder which his gallowglasses occasioned in the English capital, with their heads bare, their long hair falling over their shoulders and clipped short in front above the eyes, and clothed in saffron-dyed shirts of fine linen.

Elizabeth was less concerned with the respective claims of Shane O'Neill and the Baron of Dungannon, the former resting on Gaelic law, the latter on an English patent, than with the question of policy involved. Characteristically, she temporised; but fearing that Shane could become a tool of Spanish intriguers, she permitted him to return to Ireland, recognising him as The O'Neill. (Elizabeth's recognition of his claim to the title the O'Neill was meaningless, except symbolically, as she had no authority to confirm a title conferred under Brehon law.)

During this visit, Shane's legal claim to his father Conn Bacach's earldom was verbally confirmed and Shane was led to believe that he would be recognised as the 2nd Earl of Tyrone, though some reservation was made of the possible future rights of Hugh O'Neill, who had succeeded his brother Brian as Baron of Dungannon. Brian had been killed in a skirmish in April 1562 by Shane's tanist, Turlough Lynagh O'Neill. However, confirmation of the grant of the earldom was never delivered, and the O'Neill was compelled to defend his hegemony in Ulster when his onetime supporter Sir Henry Sidney was appointed Lord Deputy and resurrected Sussex's policy of undermining the O'Neill's authority.

War in Ulster There were at this time three powerful contemporary members of the O'Neill dynasty in Ireland—Shane O'Neill himself, Sir Turlough and Brian, 1st Baron of Dungannon. Turlough had been elected tanist (successor) when Shane was inaugurated as the O'Neill, and hoping to supplant him. During Shane's absence in London, Turlough assassinated his principal rival, Mathew's eldest son Brian, during the O'Neill's absence when rumours of his imprisonment began to circulate. On return to Ireland, the O'Neill quickly re-established his authority, and, in spite of Sussex's protestations, renewed his battle with the O'Donnells and the MacDonnells to force them to recognise O'Neill hegemony in Ulster.