Revised 18/01/2020



The "official" lineage of the O'BRIEN clan is as follows:

Oilill Olum.

Cormac Cas.

Mogh Corb.

Fear Corb.

Aonghus Tireach.

Lughaidh Meann.

Conall Eachluaith.


Lughaidh Meann.

Conall Eachluaith.



Farthann Fionn.

Eochaidh Bailldhearg.


Aodh Caomh.






[BORU301] Lorcan MacCorc became King of the Dalcassians, and died 942.

[BORU311] Cineadh (or Kennedy, [fairhead]) (eldest son of Lorcan) was a nobleman of the royal family, chief of Tuaith Muin (Thomond) the northernmost of the three principalities of Munster. He married Babhion (daughter of Arcadh, son of Murrough O'Flaherty, Lord of Moycullen i.e. Cullen's Plain, Lord of Iar Connacht (i.e. West Connaught). Cineadh was one of the principal leaders of the resistance to the Danish incursions, was later King of Thomand, and died 951.

[BORU329] Brian (born at Kincora, near Killaloe, Munster, 941) married 1. Mor (daughter of Flan O'Hyne, Prince of Hy-Fiachra Aidhne in Galway); then 2. Eachraidh (daughter of Clearbhall, who was son of Olioll Fionn); then 3. Gormflaith (or Gormla, see LEINSTER KINGS); then 4. Dubhcobhla (daughter of King Cathal O'Connor of Connaught).

Brian was born at the family seat at Kincora (Ceann Coradh, or head of the weir), overlooking the present Killaloe bridge. Brian amassed a fortune of royal tributes from lesser or vassal chieftains, consisting of cattle, timber, wine and other items, a tax known as Boroimhe Laighean. Afterwards he therefore became known as Brian boruma ("Brian of the Tributes") or simply Brian boru.

Brian became King of Thomond & Munster (978), succeeding his elder brother Mahon. Brian and Malachy united against their common enemy, the Scandinavians, and were victorious at the Battle at Glen-mama (999), when the Irish leaders slew 4,000 of the Danish supporters. Having made peace with King Sihtric of Dublin, it was agreed that Brian should marry Gormflaith (mother of King Sihtric) and Sihtric should marry Brian's daughter Slani.

Gormflaith was noted for her beauty, famed for her six marriages, had a proud and vindictive temper together with a poor moral reputation. Danish sagas record her as the “Fairest of women and most gifted in everything that was not in her own power!” Apparently she neither controlled her temper not her inclinations, and it seems her matrimonial affairs (Brian being her third husband) were not sanctioned by church law. Brian became Monarch of Ireland (1002), but Gormflaith soon deserted him.

Gormflaith, being "bitter against King Brian", instigated an alliance between Sigurd II digri (the stout) Jarl [Earl] of Orkney & Caithness and King Sihtric silkbeard of Dublin, against Brian. By this alliance, Sihtric agreed that if they killed Brian, Jarl Sigurd should marry Gormflaith and become High King of Ireland. But Gormflaith was also impossibly promised as a prize of victory to Brodir of Man, with the Dublin Kingdom for dowry. The scene was set for the battle that took place at Clontarf (Cluain-Tarbh, or the Meadow of the Bulls), on the north side of the River Tolka estuary, which flows into Dublin Bay a short distance north-east of the city.

The Battle of Clontarf took place on Good Friday, 23rd April 1014. On behalf of Ireland were Brian boru, his son Murchad (Murrough) by his 1st wife Mor, his son Donal by his 2nd wife Eachraidh, his son Donnach (Donagh) by his 3rd wife Gormflaith, and his grandson Tordelbach; Mael Seachlainn and the southern O'Neill; the Viking Ospak of Man (who had wisely defected to Brian boru at the last minute). Opposing them and with their backs to the sea, were Jarl Sigurd; the Viking Brodir of Man; Gormflaith’s brother King Mael Morda of Leinster, with his Leinstermen; and Dublin Vikings under the command of Dubhgall (brother of Sihtric silkbeard).

Sihtric himself prudently watched the fighting from behind the walls of Dublin (and continued to reign there for several more years despite the crushing defeat of the Viking alliance). During the battle, Brian's son Murchad was slain. Brian's son Donal distinguished himself in the battle and survived only to be slain at a later date by the Siol Murray in a battle fought by the Dalcassians against the Conacians. Brian’s grandson Tordelbach was accidentally drowned near the river mouth while hunting for victims. Brian’s son Donnach helped win the battle and so succeeded him. On the opposing side Jarl Sigurd died bravely in the battle, in which altogether 4,000 Irishmen and 7,000 Vikings perished.

One saga claims that the Brian swung his own sword in the front line of the battle. But he was then 73 years old, and it would seem unlikely a 73-year old man would last long at the forefront of battle. According to another saga:

"Brian deliberately took no part in the battle, because it took place on Good Friday; instead he had spent the day in prayer in a certain wood, protected only by the shield-wall of his personal retainers. Brodir of Man, fleeing in the general Viking rout, came across this tableau in the wood, burst through the shield-wall, and hacked the king to death. Brodir was quickly taken prisoner and put to a grisly death -- his belly was slit open and his intestines pulled out of him as he was led round and round an oak tree"

Yet another version states Brodir of Man was quickly killed on the spot after he had slain Brian.

His reputation was no doubt skilfully inflated by the 12th century unknown author of Cogadh Gaedhel re Gallaish [The War of the Irish with the Foreigners].

[BOR2331] Donnchad (son of King Brian & Gormflaith) became King of Munster (until 1023), High King of Ireland (1024-42), and died in Rome on a pilgrimage (1064).

[BOR2342] Darbhforgal (daughter of Donnchad) married [MACM321] King Diarmuid (see MacMOROUGH).

[BORU332] Slani (daughter of King Brian & Mor) married [DUBL331] King Sitric III silkbeard (see DUBLIN KINGDOM).

[BORU331] Turlough/Tirdelvagh (son of King Brian & Eachraidh), King of Munster (1063-86), High King of Ireland (1055-83).

[BORU341] Muircertach/Murtough (son of King Turlough), King of Munster (1086-1119), High King of Ireland (1101-19), married Dubhchobhleigh of Ossary.

[BORU352] Lafracoth (daughter of King Muircertach) married [TMOA341] Arnulf de Montgomery (see SHREWSBURY (MONTGOMERY) EARLDOM).