O'Neill (Ó Néill), Matthew (Feardorcha) (c.1510–1558), 1st baron of Dungannon , was eldest (and disputed) son of Conn Bacach O'Neill (qv), 1st earl of Tyrone, and Alison Kelly, wife of John Kelly, blacksmith of Dundalk. Probably one of the most controversial figures in sixteenth-century Gaelic Ireland, he seems to have been the child of an affair between Conn and Alison, which can perhaps be dated to about 1509–10. When he was about 16, Alison presented Matthew to Conn, who acknowledged him as his son and heir. This decision may have been influenced by a fear of Shane (Seaán) O'Neill (qv), one of his legitimate sons. The acknowledgement was a direct affront to Shane, and sowed the seeds of a long-running feud. The first annalistic reference to Matthew records his capture of Cormac Maguire (1532); the annalist singled out Matthew from his brothers, indicating that he held prominence over them by this date. His marriage (c.1536) to Joan (d. 1600), daughter of Cú Chonnacht Maguire (qv), lord of Fir Manach, also highlights Matthew's elevated position. All of his four recorded sons seem to be her children.
His status is further confirmed by surviving Tudor sources which show Matthew acting as Conn's lieutenant. In June 1542 a truce negotiated by the government between Conn and Feidhlimidh Ruadh O'Neill of the Fews shows that the latter considered Matthew his most intransigent foe. As part of Conn's rapprochement with the crown, he and Matthew were respectively granted the titles of earl of Tyrone and baron of Dungannon by Henry VIII (October 1542). They continued to pursue their traditional rights rigorously within the neighbouring lordships, and waged wars (1544–9) against Feidhlimidh Ruadh, the O'Donnells, and the Maguires. By 1549 the position of Tyrone and Dungannon had been complicated by the gradual collapse of the eastern O'Neill lordship of Clandeboye (Clann Aodha Buidhe), the rise of Turlough Luineach O'Neill (qv), and the devastating raids launched by Sir Nicholas Bagenal (qv) on Tír Eóghain. In November 1550 Tyrone outlined his grievances before the Dublin council concerning the actions of certain army commanders, but was branded a traitor by some councillors.
During this period Dungannon seems to have attempted to strengthen his position. Tyrone with Shane launched unexpected attacks on Dungannon and other familial rivals in summer 1551. In the autumn Dungannon was in the ascendant and declared himself the king's man. Now at his zenith, Dungannon, with the help of Bagenal, managed to procure Tyrone's arrest by the lord deputy, James Croft (qv). Despite his success, he narrowly missed his chance to kill Shane, and from October 1551 was forced to rely on Tudor military support to maintain himself. Dungannon's heavy defeat by Shane, while conveying reinforcements to Croft in summer 1552, signalled the virtual collapse of his power.
In the middle of the 1550s Dungannon and Tyrone realigned themselves against Shane, and mounted attacks on Shane's mercenary allies, the MacDonnells. Shane, however, was too wily for them and steadily drained their diminishing strength, expelling them to the Pale in 1557. They quickly returned to Tír Eóghain with Tudor support after Shane's defeat by An Calbhach O'Donnell (qv), lord of Tír Conaill, that year. Realising the vulnerability of his position, Shane succeeded in having Dungannon assassinated in 1558, prompting Tyrone's flight to the safety of the Pale.
Dungannon's controversial life and death shaped the politics of the great O'Neill dynasty in the last seven decades of the sixteenth century. Considerable doubts remain whether he was the natural son of Tyrone. But pretender or not, Tyrone's acknowledgement of him made Shane justifiably aggrieved. In any case, the recognition paved the way for the career of Dungannon, who showed good political acumen in exploiting his fortuitous position. The turbulence within the O'Neill dynasty cannot be solely attributed to Dungannon. It must be laid at the feet of Tyrone, for without his acknowledgement Matthew O'Neill would have remained Matthew Kelly.