Tadhg na Mainistreach Mac Carthaigh Mór reigned as King of Desmond from 1390/2 to his death in 1428. He was the son of the previous king Domhnall Óg Mac Carthaigh Mór (r. 1359–1390/2). According to the Annals of Inisfallen

Annals of Inisfallen

The Annals of Inisfallen are a chronicle of the medieval history of Ireland. There are more than 2,500 entries spanning the years between AD 433 and AD 1450, but it is believed to have been written between the 12th and 15th centuries...

Tadhg Mac Carthaigh had the reputation as the greatest wine-drinker in Ireland when he died, but was still "a son worthy of his father." He was married to one Sebán, a daughter of "Garret the earl," but whether this refers to the Earl of Kildare

Gerald FitzGerald, 5th Earl of Kildare

-Background:Kildare was the son of Maurice FitzGerald, 4th Earl of Kildare and Elizabeth Burghersh.-Family:Kildare married, firstly, Margaret Rocheford, daughter of Sir John Rocheford. Their children included: *Thomas FitzGerald....

 or Earl of Desmond

Gerald FitzGerald, 3rd Earl of Desmond

Gerald fitzMaurice FitzGerald, also known by the Irish Gaelic "Gearóid Iarla" , was the 3rd Earl of Desmond, in southwestern Ireland, under the first creation of that title, and a member of the Hiberno-Norman dynasty of the FitzGeralds, or Geraldines...

 is uncertain.

Mac Carthaigh was among those Irish kings and princes to submit to Richard II of England

Richard II of England

Richard II was King of England, a member of the House of Plantagenet and the last of its main-line kings. He ruled from 1377 until he was deposed in 1399. Richard was a son of Edward, the Black Prince, and was born during the reign of his grandfather, Edward III...

 in his progress of 1394, after which the title King of Desmond was rarely used by later members of the dynasty, the title of Mac Carthaigh Mór (Prince of Desmond) becoming the preferred.

After dying in Ballycarbery Castle

Ballycarbery Castle

Ballycarbery Castle is a castle 3km from Cahersiveen, County Kerry, Ireland . The castle is situated high on a grass hill facing the sea and is a short distance from Cahergall Fort and Leacanabuile Fort.-History:...

, Tadhg was buried in the monastery there, while his wife Sebán died in Caislén Mac nAeducáin and was buried at Tráig Lí. He was succeeded by his son Domhnall an Duna Mac Carthaigh Mór, but in recent times his younger son Cormac of Dunguile has frequently been mentioned as the ancestor of the Sliocht Cormaic of Dunguile

Sliocht Cormaic of Dunguile

The Sliocht Cormaic of Dunguile, otherwise known as the MacCarthys of Srugrena Abbey, or the Srugrena sept, as well as the Trant McCarthys, are the principal and today perhaps only known surviving sept of the MacCarthy Mór dynasty, the Kings of Desmond...

, the senior or today perhaps only surviving sept

Sept

A sept is an English word for a division of a family, especially a division of a clan. The word might have its origin from Latin saeptum "enclosure, fold", or it can be an alteration of sect.The term is found in both Ireland and Scotland...

 of the MacCarthy Mór dynasty

MacCarthy dynasty

The MacCarthy dynasty was one of Ireland's greatest medieval dynasties. It was and continues to be divided into several great branches. The MacCarthy Reagh, MacCarthy of Muskerry, and MacCarthy of Duhallow dynasties were the three most important of these, after the central or MacCarthy Mór...

.

His epithet "na Mainistreach" means "of the monastery."