O'Connor (Ó Conchobair), Toirrdelbach (d. 1345), king of Connacht, was son of Áed mac Eógain O'Connor (qv), king of Connacht, and of a daughter of Toirrdelbach O'Brien (Ó Briain). After the death of his half-brother Fedlimid (qv), king of Connacht, at the battle of Athenry (10 August 1316), Toirrdelbach assumed his claims to the Connacht kingship. However, he did not succeed his fallen half-brother; instead, the kingship passed to their cousin Ruaidrí ‘na Fed’ (of the Faes). The new king's position was weakened by a Burke offensive, which secured his submission before the end of 1316. No doubt this battering exposed the fragility of Ruaidrí's power, allowing Maolruanaidh MacDermott (qv) (Mac Diarmata) to depose him and raise Toirrdelbach to the kingship early in 1317. Later, in his submission of March 1318 to the lord lieutenant, Roger Mortimer (qv), Toirrdelbach's power was confirmed, as he was described as princeps Hibernicorum Connacie (head or prince of the Irish of Connacht). Moreover, he was also granted the lands of Síl Muiredaig, Tirmany, and the Faes from the crown. In an attempt later that year to further consolidate his power, he sought to subdue more fully Cathal O'Connor (qv) of the Sligo-based Clann Aindrias. In spite of Cathal's offers to recognise his suzerainty, Toirrdelbach and MacDermot were determined on forcefully imprinting their hegemony, compelling Cathal to fight. They made a major mistake, as he routed their forces, took Toirrdelbach's kingship, and retained it till the latter killed him (26 September 1324).
Toirrdelbach's second reign faced a serious threat from Walter de Burgh (qv), the probable Connacht representative of Richard de Burgh (qv), the Red Earl of Ulster. This led to years of fighting with Walter's family, the MacWilliam Burkes. Fortunately, Toirrdelbach secured the support of the Red Earl's successor as earl, William de Burgh (qv). Indeed, Toirrdelbach campaigned in 1328 with Earl William and Muirchertach O'Brien (qv), king of Thomond, against Brian Bán O'Brien (qv) in Tipperary, meeting with defeat. But from the late 1320s Toirrdelbach's relationship with the MacDermots gradually deteriorated. And in 1332 Walter Burke was captured by Earl William, who starved him to death in Northburgh castle, Inishowen. During the following year, Earl William was assassinated, leaving only a daughter as an heir. This left Toirrdelbach in a very powerful position, and he joined the O'Briens to fight the MacNamaras (Meic Conmara) during 1334. In 1335 the Burke lordship in Connacht fell under the sway of Edmund and Richard Burke, leaders of the Clanricard branch. However, their dominance had to contend with the revenge of Sir Edmund Albanach de Burgh (qv), Walter's brother. In this struggle Toirrdelbach remained close to the Clanricard branch, earning the enmity of Edmund Albanach. And by 1337 Toirrdelbach was building a castle at Athleague to check any expansion of Edmund Albanach. However, the latter had his revenge in 1338, drowning Edmund of Clanricard in Lough Mask. Toirrdelbach became his avenger. After the death (1335) of his first wife, Fionnuala, daughter of Muirchertach O'Brien (qv) (d. 1343), Toirrdelbach established an alliance with the O'Donnells (Uí Domnaill) of Donegal, marrying Derbail (d. 1343), daughter of Áed O'Donnell. But in 1339 Toirrdelbach put Derbain away, breaking the O'Donnell alliance, and married his own maternal aunt Sláine (d. 1343), daughter of Toirrdelbach O'Brien. She was also the widow of Edmund of Clanricard, which explains why Toirrdelbach had expelled Sir Edmund Albanach from Connacht to the islands during 1338.
From there Edmund Albanach waged a naval war for some time, but by 1340 he had secured his pardon and had reestablished himself in Connacht. This did not prevent Toirrdelbach from steeling his grip on his kingdom, interfering among the O'Kellys (Uí Chellaig) in 1340, and capturing Roscommon castle the following year. But in 1342 Toirrdelbach fell out with Conchobhar MacDermot, leading to his overthrow by Sir Edmund Albanach, MacDermot, and Aodh O'Connor of Clann Muirchertaig Muimnig. Toirrdelbach resumed his kingship in 1343 and held it till his death in a skirmish (1345) with Clann Muirchertaig Muimnig. This great king was succeeded as king of Connacht by his son, Aed (d. 1356). In 1350 Aed was deposed by Sir Edmund Albanach and replaced with Aodh O'Connor of the Clann Muirchertaig Muimnig. His kingship was brief, as Aed returned and expelled him. However, Aed's reign ended abruptly in 1356 when Donnchad Carrach O'Kelly killed him for eloping with his wife.