MacMurrough Kavanagh (Mac Murchadha Caomhánach), Art Mór (1357–1416/17), king of Leinster, second son of Art MacMurrough (qv), king of Leinster, and a daughter of Philip O'Byrne. Little is known of his early life. At first he recognised the primacy of his cousin Art son of Diarmait, but after his uncle Donnchadh MacMurrough, king of Leinster, was killed in 1375, he became a leading figure of his dynasty, and, taking advantage of MacMurrough advances into the Barrow valley and the midlands, was able to develop and consolidate a diplomatic web that stretched from the Leinster mountains to Arra in Tipperary. Described as a tall handsome man with a stern countenance, Art built his strength, like no other Leinster ruler before him, by drawing mercenaries and allies from this pool, and his charisma won him many friends among the Gaelic kings. He also capitalised on the weakness of the colonial government in the later 1370s, and his dominance along the Barrow, through which the royal highway ran, was acknowledged by the English in 1379, in which year he was appointed keeper of the roads between Carlow and Kilkenny, and awarded a fee of 80 marks. By 1381 he had outmanoeuvred his dynastic rivals by coercion and execution and was acknowledged as king of Leinster.
Art's marriage of about 1390 to Elizabeth Calf (qv), heir of Norragh, set him on a collision course with the English. The Statutes of Kilkenny prohibited unlicensed mixed marriages and consequently Elizabeth's lands were forfeit. In 1391 Art petitioned to have this decision reversed, and when this approach failed he devastated Carlow and Kildare in 1392. Shortly afterwards Norragh's revenues were restored to Elizabeth.
On 2 October 1394 Richard II (qv) landed at Waterford determined to arrest the colony's decline. MacMurrough greeted his arrival by plundering New Ross, but Richard's army proved too powerful for him and by 30 October he had submitted. He was briefly imprisoned on charges brought by James Butler (qv), 3rd earl of Ormond. On 7 January 1395 MacMurrough and O'Byrne sealed an indenture agreeing to vacate Leinster and conquer fresh territories from the rebel Irish as royal mercenaries. In return Richard restored Norragh to Elizabeth. The acceptance of the agreement by many Leinster nobles on 16 February 1395 confirms the widespread support for Art's kingship. Before departing for England, Richard elated by his success, brought Art to Dublin where he was knighted in March.
The Leinstermen remained at peace until 1396, but Art became disaffected because Ormond resurrected old claims to lands in Wicklow and also because an attempt was made to kidnap him at Dublin during 1397. Art's enemies gained military support from the justiciar Roger Mortimer (qv). The struggle culminated in Mortimer's defeat and death in battle on 10 June 1398, in which he was opposed by a force led by O'Byrne, which included MacMurrough's captain of kerne. On hearing of Mortimer's death, Richard decided on a second expedition to Ireland, and before leaving England he granted Norragh to the earl of Surrey. Richard landed at Waterford on 1 June 1399; in spite of initial success, he could not bring MacMurrough to battle and pursued him into the Leinster mountains. This ill-considered adventure was a disaster as MacMurrough, from this protecting environment, ceaselessly harried the English. At a failed parley MacMurrough told Richard's envoy that he would never submit. Despite Richard's best efforts to capture him, Art remained at liberty, and, having promised Elizabeth that he would not rest until her lands were restored, refused to make peace; he even aided Desmond against Ormond in Munster.
After Richard's departure on 27 July 1399, Art resumed his routine of extracting black rents from the towns of the south-east. There is a strong possibility that a letter from Owain Glyndwr, urging Irish kings to join him in a struggle against the English, which was captured at Waterford, was meant for Art. Throughout the first decade of the fifteenth century, Art cemented his power, but in his last years his military strength declined and his sons lacked his ability. Significantly during this period Art and the Butlers became allies, as evidenced by the marriage of Art's eldest son Donnchadh MacMurrough (d. 1478) to Aveline Butler, half-sister of James Butler (qv), 4th earl of Ormond, perhaps in reaction to the arrival of Ormond's enemy John Talbot (qv), Lord Furnival, in Ireland as lord lieutenant during 1414. These events provide the context for Art's attack in 1416 on the Talbot liberty of Wexford.
The annals are divided over the date and circumstance of MacMurrough's death. One account records that he died in his bed in December 1416, while another tells that he died of poisoning in his sixtieth year in January 1417. The reign of his son Donnchadh was disturbed. In 1419 he was captured by Talbot and imprisoned in the Tower of London, where he remained until 1427, when he was returned to Ireland to curb the activities of his brother Gerald. He was present on an English campaign against O'Byrne in 1428, but renounced his reformed ways by burning Naas in September 1429. However, his military weakness meant that he reestablished himself as MacMurrough overlord only after Gerald's death in 1431.
Donnchadh's kingship was dominated by wars with O'Byrnes and an unhealthy dependence on Ormond. The killing of his heir Muircheartach by the English of Wexford in 1442 probably sparked the dynastic struggle with his nephews, Gerald's sons, in 1444. By 1447 Donnchadh was reconciled with his nephew, Domhnall Riabhach MacMurrough (qv), whom he recognised as his successor. Domhnall's position as heir designate was made clear by his representing Donnchadh during a submission to Richard (qv), duke of York, in August 1449. This arrangement worked well and both of them, with the Butlers, attacked Wexford in 1454. Shortly afterwards Donnchadh, perhaps because of declining eyesight, stepped aside for Domhnall; he died eventually in 1478.