The accepted date for the birth of Brian Boru is 941, not 925 as stated by the Four Masters. According to Eleanor Hull's History of Ireland (p. 201) the first O'Brien to adopt the surname was Donogh Cairbre (1194-1242), son of Donal, who submitted to Henry II. Murrough O'Brien (d. 1551) was first Earl of Thomond.

Ó Briain A Dalcassian sept, deriving its name and importance from the family of King Brian Boru. Now very numerous in other provinces as well as Munster.

Bibl; IF 62, etc, etc; MIF 245; SIF 156; Map Clare, Lim, Tip, Wat; Plate II

(Celtic) the Irish O'Briain = DesCENDANT OF Brian [v. O-’, and + the genit. of Brian, q.v.]

(Celtic) the Irish O'Briain = DesCENDANT OF Brian

(Irish) Granson of Bryan or Brian (hill).

The O'Briens of Thomond took their name from the monarch Brian Boru, who was slain at the battle of Clontarf in 1014. O'Donovan.

O'BRIEN: The descendant of Brien, i. e., exalted, noble.

(Irish), Descendant of Brien; i. e., Brien Boiroimhe, King of Ireland, A.D. 1002. O'Connor, Descendant of Con­nor, King of Connaught. O'Kelly, Descendant of Cellach, Prince of the Ui Many in the ninth century. O'Neill, De­scendant of Neill, or Niall Noygiollach, Niall of the Nine hos­tages, or Niall the great, Monarch of Ireland in the fourth century.

The surname O’Brian comes from the Irish Gaelic O’Briain, which means ‘son of Brian’. Brian is an ancient Celtic name of uncertain origin-but the most likely explanation is that it means ‘hill’.

The family clans of the O’Brians have great importance in Ireland. This is mainly due to their illustrious predecessor, the great Brian Born, King of Leinster and Munster, who fought the Vikings at the Battle of Clontarf.

The O’Brians were originally found mainly in Munster, but are now numerous all over Ireland, and indeed wherever Irishmen have immigrated. It is not unexpected to find the name O’Brian occurring frequently in London, Boston, or Sydney, but a little-known fact is that one of the great wines of France-Chateau Haut Brian-is in fact derived from the Irish O’Brian. (The O’Brians are not the only Irish to have distinguished themselves in this most French of preserves-witness the Hennessys of Cognac fame.) In some cases the Irish O’Brian is derived from O’Byrne (see Byrne), derived from O’Biorain. Also, during the centuries of British persecution in Ireland, many Irish O’Brians found it prudent to anglicise their name to Byran, Bryon or Bryom: compare the case of the Byrnes, above. In other cases it is a derivation of the first name Brian, which in this instance came to England with the Norman Conquest, being found in Latinised form in the Domesday Book, and giving rise to a number of variant English surnames such as Bryant and Byrne. Thus the Irish who switched from O’Brian to Bryan were really doing little more than completing a circle of variations.

The O’Briens have produced several Irish literary figures during this century. The novelist Edna O’Brien (b. 1932) is famed for her romantic portrayals of her childhood in remote County Clare. The humorist Flann O’Brien (1911— 66), whose real name was Brian O’Nolan, is best remembered for his hilarious novel At Swim-Two-Birds. Conor Cruise O’Brien (b. 1917) is a politician and journalist, as well as a biographer. He served as UN representative in the Congo during the Katanga crisis, and is now editor of the Observer.

Special effects genius Willis O’Brien gave birth to one of the screen’s greatest stars, King Kong. His brilliant stop-animation techniques reached a peak with the climactic battle with aircraft atop the Empire State Building-one of the most memorable scenes in cinema history. O’Brien’s handiwork was unsurpassed 43 years later, when Dino De Laurentiis, employing the latest technology, resurrected the giant ape. A laudable attempt, the second ape wasn’t a patch on the strangely charming original.

Place and major geographic feature names related to O’Brien are rare. The United Kingdom has none. Ireland has 2 towns-O’Briensbridge and O’Briens Town, while Canada has one town called simply O’Brien.

With about 35,000 namesakes O’Brien is Ireland’s 6th most popular surname. Thus about one out of every 135 residents of Ireland is an O’Brien. (The name is not common enough throughout England, Scotland and Wales to be counted separately.) Around the world O’Briens are most common in Canberra (one in 500 families), Melbourne (one in 785) and Brisbane (one in 887). The United States has an estimated total of just under 133,000 O’Briens-this makes it their 195th most popular surname.