Cathair Mór son of Fedlimid Fir Urglais, a descendant of Mug Corb, was, according to medieval Irish legend and historical tradition, a High King of Ireland

High King of Ireland

The High Kings of Ireland were sometimes historical and sometimes legendary figures who had, or who are claimed to have had, lordship over the whole of Ireland. Medieval and early modern Irish literature portrays an almost unbroken sequence of High Kings, ruling from Tara over a hierarchy of...

. He took power after the death of Fedlimid Rechtmar

Fedlimid Rechtmar

Fedlimid Rechtmar or Rechtaid son of Tuathal Techtmar, was, according to medieval Irish legend and historical tradition, a High King of Ireland. His mother was Báine, daughter of Scál. He took power after killing his predecessor, and his father's killer, Mal mac Rochride...

. He is said to have had thirty sons, but only ten of them had children; several medieval dynasties of Leinster

Leinster

Leinster is one of the Provinces of Ireland situated in the east of Ireland. It comprises the ancient Kingdoms of Mide, Osraige and Leinster. Following the Norman invasion of Ireland, the historic fifths of Leinster and Mide gradually merged, mainly due to the impact of the Pale, which straddled...

 traced their ancestors to them. His daughter Cochrann was said to have been the mother of the fenian

Fenian Cycle

The Fenian Cycle , also referred to as the Ossianic Cycle after its narrator Oisín, is a body of prose and verse centering on the exploits of the mythical hero Fionn mac Cumhaill and his warriors the Fianna. It is one of the four major cycles of Irish mythology along with the Mythological Cycle,...

 hero Diarmuid Ua Duibhne

Diarmuid Ua Duibhne

Diarmuid Ua Duibhne or Diarmid O'Dyna is a son of Donn and a warrior of the Fianna in the Fenian Cycle of Irish mythology. He is most famous as the lover of Gráinne, the intended wife of Fianna leader Fionn mac Cumhaill in The Pursuit of Diarmuid and Gráinne...

.

He features in the saga Esnada Tige Buchet ("The Melody of the House of Buchet"). Cathair's daughter Eithne Tháebfhota is fostered

Fosterage

Fosterage, the practice of a family bringing up a child not their own, differs from adoption in that the child's parents, not the foster-parents, remain the acknowledged parents. In many modern western societies foster care can be organised by the state to care for children with troubled family...

 by a hospitable Leinsterman named Buchet who has many herds of cattle, but Cathair's sons so exploit Buchet's hospitality that he is left with only one bull and seven cows, and the king, now old and enfeebled, is unable to restrain them. Buchet and his family, including Eithne, are reduced to living in a hut in the forest in Kells, County Meath

Kells, County Meath

Kells is a town in County Meath, Ireland. The town lies off the M3 motorway, from Navan and from Dublin. In recent years Kells has grown greatly with many Dublin commuters moving to the town....

. Later, when Cormac mac Airt

Cormac mac Airt

Cormac mac Airt , also known as Cormac ua Cuinn or Cormac Ulfada , was, according to medieval Irish legend and historical tradition, a High King of Ireland...

 is king, he marries Eithne and restores Buchet's fortunes (in other stories the king who marries Eithne is Cathair's successor Conn Cétchathach). In another saga, Fotha Catha Cnucha ("The Cause of the Battle of Cnucha"), Cathair gives the hill of Almu (Knockaulin, County Kildare

County Kildare

County Kildare is a county in Ireland. It is part of the Mid-East Region and is also located in the province of Leinster. It is named after the town of Kildare. Kildare County Council is the local authority for the county...

) to the druid

Druid

A druid was a member of the priestly class in Britain, Ireland, and Gaul, and possibly other parts of Celtic western Europe, during the Iron Age....

 Nuada son of Aichi. This hill will later be famous as the home of Nuada's great grandson Fionn mac Cumhaill

Fionn mac Cumhaill

Fionn mac Cumhaill , known in English as Finn McCool, was a mythical hunter-warrior of Irish mythology, occurring also in the mythologies of Scotland and the Isle of Man...

.

Cathair ruled for three years, at the end of which he was killed by the Luaigne of Tara

Hill of Tara

The Hill of Tara , located near the River Boyne, is an archaeological complex that runs between Navan and Dunshaughlin in County Meath, Leinster, Ireland...

, led by Conn Cétchathach. The Lebor Gabála Érenn

Lebor Gabála Érenn

Lebor Gabála Érenn is the Middle Irish title of a loose collection of poems and prose narratives recounting the mythical origins and history of the Irish from the creation of the world down to the Middle Ages...

synchronises his reign with that of the Roman emperor

Roman Emperor

The Roman emperor was the ruler of the Roman State during the imperial period . The Romans had no single term for the office although at any given time, a given title was associated with the emperor...

 Marcus Aurelius (161-180). The chronology of Geoffrey Keating

Geoffrey Keating

Seathrún Céitinn, known in English as Geoffrey Keating, was a 17th century Irish Roman Catholic priest, poet and historian. He was born in County Tipperary c. 1569, and died c. 1644...

's Foras Feasa ar Éirinn dates his reign to 113-116, that of the Annals of the Four Masters

Annals of the Four Masters

The Annals of the Kingdom of Ireland or the Annals of the Four Masters are a chronicle of medieval Irish history...

to 119-122.