O'Sullivan Beare, Domhnall (1560–1618), Gaelic lord and soldier, was son of Domhnall Cam O'Sullivan Beare, lord of Beare and Bantry, and Margaret O'Brien, daughter of O'Brien of Thomond. After the murder of Domhnall Cam by the MacGillacuddys (1563), his younger brother Sir Eóghan took his place as lord of Beare and Bantry. The first reference to Domhnall comes in 1581, when he defeated the combined raiders of Diarmait O'Donovan and Capt. John Zouche. In 1587 he disputed his uncle's title under English law to Beare and Bantry. The commissioners appointed to investigate the case found in favour of Domhnall, and bestowed on him Beare and the castle of Dunboy (1593). In the following year he succeeded his uncle as the titular O'Sullivan Beare on the latter's death.
After the Nine Years War broke out in 1594, he became a partisan of Hugh O'Neill (qv), 2nd earl of Tyrone. However, the Four Masters point out that Domhnall did not attend on Tyrone or give him hostages during his progress through Munster in the early months of 1600. When the Spanish landed at Kinsale (September 1601) Domhnall offered them 2,000 fighting men. He housed a Spanish garrison of sixty soldiers under Capt. Saavedea in his castle of Dunboy, supplying them with two months provisions. At the council before the battle of Kinsale, Domhnall sided with Tyrone in his opposition to the ill-fated proposal of Red Hugh O'Donnell (qv) to launch a night attack on the English army. After the defeat (24 December 1601) Tyrone and O'Donnell appointed Domhnall supreme commander of the Munster forces. In this capacity he offered to relieve the Spanish in Kinsale, but his offer was refused. By the terms of the Spanish surrender on 2 January 1602, Domhnall's castle of Dunboy was included. This he ignored, and waged an effective war on the crown forces from this fortress and the wild terrain around Glengarriff. This prompted a full-scale assault by Sir George Carew (qv), lord president of Munster, who besieged Dunboy with the help of the sons of Sir Eóghan on 6 June 1602. Domhall was at Ardea, a day's march away, awaiting a Spanish ship. In his absence, Carew took Dunboy after a protracted siege caused by the obstinate resistance of the garrison, killing its constable and executing the twenty-seven survivors in late June 1602.
Domhnall continued to fight, but his situation was militarily hopeless by December 1602. At this point he decided to march to the relative safety of Ulster. On New Year's day 1603 his force of 1,000 set out from Glengarriff. Throughout their trek through north Cork, Limerick, and Tipperary they were attacked continually by pursuing English forces and local Irish, suffering many casualties from these attacks and from the wintry conditions. On the eighth day of the march they reached a crossing point on the Shannon in the modern townland of Portland in the Tipperary barony of Lower Ormond. There they were savagely attacked by Donnchadh MacEgan, sheriff of Tipperary, who was determined to prevent their crossing into Connacht. Despite warnings from Domhnall, MacEgan persisted in his assault and was killed. On the banks of the Shannon they slaughtered and skinned their remaining horses to make coracles to cross the river. Once across they marched on to Aughrim, Co. Galway, only to find their way blocked by Capt. Henry Malby and Sir Thomas Burke. Realising that he could not avoid them, Domhnall threw his outnumbered but desperate men in a do-or-die assault on the enemy, killing Malby and routing his troops. This victory convinced many pursuers to cease the chase, and Domhnall's followers escaped into the forests of Breifne. On 14 January 1603 he and thirty-four survivors arrived at the castle of Brian Óg O'Rourke (qv) at Leitrim. They rested there about a week before marching into Ulster.
In June 1603 he accompanied Ruaidhrí O'Donnell (qv) and Tyrone to Hampton Court to see James I. However, he failed to make his peace and took ship for Spain. There he was graciously received by Philip III, who bestowed on him the title of count of Birhaven and a monthly pension of 300 gold pieces. In 1607 he was honoured further by being made the first Irish knight of the order of Santiago. His end came as the result of a duel between John Bathe (qv) and his cousin, Don Philip O'Sullivan Beare (qv) in Madrid (16 July 1618 ). According to the O'Sullivan version of a very problematic incident, Philip took exception to Bathe's insulting comments about Domhnall, and challenged him to a duel. As Philip was about to kill Bathe, Domhnall intervened to save him but Bathe stabbed him fatally in the throat.
Domhnall's skill as a soldier and his remarkable ability as a leader have ensured his place as one of the most celebrated Irish soldiers of the sixteenth century. He married (date uncertain) Elena, daughter of O'Sullivan Mór; they had two sons.