Thanks to the Irish diaspora that began in earnest in the mid-19th century – when Ireland’s population was cut in half by the Great Hunger, with over a million people fleeing the famine to seek safety overseas – Irish family names proliferate all over the world. Most, if not all, can be traced to ancient clans or dynasties, whose lineages stretch right back through the medieval era, to a time when surnames were very first used.
The tales associated with these names are straight out of Game of Thrones, full of fighting between royal Gaelic families and breakaway septs of big clans, constantly battling and betraying one another, not to mention warring with Viking invaders, scrapping with Anglo-Norman forces and going toe-to-toe with armies sent by rapacious English monarchs.
What were the main kingdoms of Ireland?
The island of Ireland was once divided into many small kingdoms, as well as larger provinces, the main four being (as now) Leinster, Munster, Ulster and Connaught. Clan chiefs vied for control of these dominions, as well as for the loftiest position in the land: High King of Ireland.
What's the most common Irish surname?
The most common Irish name of all, Murphy, can be linked to several clans and people that used the moniker Mac Murchada (which derives from the Old Irish words for ‘sea warrior’, and was anglicised as Murphy), including the infamous Diarmait Mac Murchada. However, most surnames can be more accurately traced to a specific clan, king or sept leader, including the following big players.
How were Irish clans organised?
Many people associate clans with Scotland, but the word – which derives from the Irish clann (meaning children) and is used to describe a highly organised hierarchal family grouping – originated in Ireland in the early Middle Ages. A patriarchal kinship system, Irish clans were led by the male head of the family, the Taoiseach (a title still given to Ireland’s Prime Minister), with the pecking order of other clan members determined by their blood relationship to this chieftain.
The Old Irish word for family is fine, and the system recognised several levels of kinship: Gelfine (those who share a common grandfather with the chief), Derbfine (common great grand father), Larfine (common great great grand father) and Indfine (common great great great grand father). When a chieftain died, instead of the eldest son assuming the role, a new leader was elected from and by the higher ranks of this tanistry system. Sometimes a successor had already been pre-decided, and this heir-apparent/second in command was known as the Tánaiste, which remains the title used for Ireland's Deputy Prime Minister. The hierarchy was also an important way of determining property inheritance after the death of a leader.
It wasn't unusual for the male siblings or sons of successful chieftains to break away and form their own clan or sept (from the Irish sliocht, meaning birth or line), which would then adopt a name relating to the founding patriarch. For this reason, Irish clans closely related by blood could have different names and co-exist, with members simultaneously having a claim to hierarchal status in the original clan.
There were also ceremonial positions within Irish clans, including the 'bard', who would recount stories about the group’s heroic achievements, and regularly recite the genealogy of the group, so everyone could remember who was who, and where they sat in the bloodline (all very important in a time of oral storytelling and constant conflict, where people died young and new leaders had to be appointed on a regular basis).
What's the difference between Irish and Scottish clans?
Irish clans are more closely tied to family groups than Scottish clans (non-family members were able to join Scottish clans by swearing fealty to the chief and sometimes adopting the name, but this didn't happen in Ireland). Irish clans are also more closely connected to the county or province where they originated, and the lines of succession and loyalty were different, being determined according to ancient Brehon Laws (which date back at least as far as the 5th century).
6 most powerful Irish clans
The O'Neills
Variations: O'Neil, O'Niall, O'Neall, O'Neal, Neill
Irish name: Ua Néill
Meaning: Descendants of Niall
Parent dynasty: Uí Néill
Province: Ulster
Founder: Flaithbertach Ua Néill
Historic seat of power: Shane’s Castle, Edenduffcarrick, Antrim
The O'Neill Clan were part of the northern Uí Néill dynasty, claiming direct descent from Niall of the Nine Hostages (Niall Noígíallach), an Irish king who is believed to have existed in the 5th century, but whose story is so surrounded by myth that it's impossible to separate fact from legend.
Although the clan was founded by Flaithbertach Ua Néill, it’s named after his great, great grandfather Niall Glúndub, who was a High King of Ireland in the 10th century (as was Flaithbertach's grandfather Domhnall ua Néill).
Having benefited from the Norman invasion of Ireland, which dislodged several rival clans, the O'Neills accumulated territory and power, and from 1230s ruled the kingdom of Tír Eógain in Ulster, which encompassed most of the modern counties of Tyrone, Derry and Antrim. Over the centuries, several septs of the clan went their own way, including the O'Neills of Clanaboy.
The final family chief, Hugh O'Neill, Earl of Tyrone, fought against the English with the clan's erstwhile enemies, the O'Donnells, during the Nine Years' War. When that finished in defeat (spelling the end of the clan system in Ireland) he joined Rory O'Donnell to relocate to continental Europe during the Flight of the Earls in 1607. O'Neill remains one of the 10 most common surnames in Ireland.
The O'Donnells
Variations: O'Donle, O'Donall
Irish names: Ó Dónaill, Ó Domhnaill, Ó Doṁnaill, Ua Domaill
Meaning: Descendant of Dónal
Parent dynasty: Uí Néill
Province: Ulster
Founder: Conall Gulban
Historic seat of power: Donegal Castle
In medieval and early modern Ireland, the O'Donnells ruled over the Kingdom of Tyrconnell (Tír Conaill) in Ulster, a territory that covered most of the modern county Donegal (except the Inishowen Peninsula) plus parts of Sligo, Leitrim, Fermanagh and Derry. The clan was founded in 1248 by Gofraid O'Donnell (Gofraidh Ó Domhnaill), son of Donal Mor O'Donnell.
A highly successful family, they fought regularly with their equally powerful neighbours, the O'Neills, for dominance of Ulster and northern Connacht (even though both clans descended from the same Uí Néill dynasty).
Gofraidh drove the Normans from northern Connacht with victory at the 1257 Battle of Creadran-Cille, where he killed Maurice FitzGerald, 2nd Lord of Offaly, in one-to-one combat. O'Donnell subsequently died from wounds received in this duel, but not before he was carried into another fight by his clansmen, who defeated the forces of Brian O'Neill.
More battles with the O'Neills followed, until they found a common enemy. During the Nine Years' War (1593–1603), Prince Red Hugh O'Donnell allied with Hugh O'Neill to fight the English. They were defeated at the Battle of Kinsale in 1601, and although the Stuart king King James VI and I pardoned Rory O'Donnell and named him Earl of Tyrconnell, he left the country in the 1607 Flight of the Earls, and Tyrconnell was colonised as part of the Plantation of Ulster.
The O'Briens
Variations: Brien, O'Bryan, O'Brian, Brian, O'Brine, O'Bryen
Irish names: Uí Briain or Ó Briain
Meaning: Descendant of Brian
Parent dynasty: Dál gCais
Province: Munster
Founder: Brian Boru
Historic seat of power: Bunratty Castle, County Clare
Founded and named after one of medieval Ireland’s most influential and famous characters, Brian Boru, the O'Briens are a sept of the Dál gCais, an older clan that, until the 10th century, ruled a relatively modest area in modern-day County Clare.
As chief, Brian's father, Cennétig mac Lorcáin, expanded the territory across the River Shannon, capturing parts of Limerick and becoming King of Thomond. Brian was the youngest of 12 sons, and his elder brother Mathgamain became king when Cennétig died. Brian battled alongside his brother, fighting not only rival clans for control of Cashel (Munster’s symbolic capital), but also Viking forces who’d murdered their mother and several other brothers.
When Mathgamain was slain by Máel Muad mac Brain, King of Munster, Brian was crowned King of Thomond. He avenged his brother’s death, killing Máel Muad and becoming King of Munster. Through various campaigns, conquests, cunning plans and alliances, Brian ascended to the position of High King of Ireland in 1002, and is credited with uniting large parts of the country and vanquishing Viking power.
During the Battle of Clontarf near Dublin in 1014, Brian's army defeated the combined forces of Máel Morda (former King of Leinster) and Norse leaders from Dublin, Scotland and the Isle of Man, but he was killed, along with much of his bloodline. The O'Briens retained power in Munster for several generations, however, and two more members of the sept later became High Kings of Ireland. The family territory was eventually reduced to Thomond (the Kingdom of Limerick), which they ruled until 1542, when Murrough Ó Briain surrendered his sovereignty to England's King Henry VIII.
The O'Connors
Variations: Connor, Conor, Connors, MacConnor, McConnor
Irish names: Ó Conchobhair or Ó Conchúir
Meaning: Descendant of Conchúr
Parent dynasty: Uí Briúin Ai / Síl Muiredaig
Province: Connacht
Founder: Conchobar mac Taidg Mór
Historic seat of power: Clonalis House, Castlerea, Co. Roscommon
The O'Connors ruled the Kingdom of Connacht from 967 for the most of the following 500 years. The clan was founded in the 9th century by Conchobar mac Taidg Mór, who hailed from the Uí Briúin branch of the Connachta – one of several royal dynasties that claimed a direct connection to the legendary High King Conn Cétchathach (Conn of the Hundred Battles).
Notable members of the O'Connor clan include Tairrdelbach Ua Conchobair (great, great grandson of Brian Boru through his mother), who reigned as King of Connacht for over 50 years (1106–1156) and was High King of Ireland from 1120 until 1156, after he defeated and partitioned the Kingdom of Munster, shaking the O'Brien sect's long-lasting hold on the High Kingship.
Tairrdelbach had more than 20 sons – who fought, killed, betrayed and blinded one another until one, Ruadhrí mac Tairrdelbach Ua Conchobhair, rose to prominence and was anointed as his father's Tánaiste.
Ruaidrí was crowned King of Connacht in 1156, and subsequently became the last High King of Ireland in 1166, his reign ending with the Anglo–Norman invasion in 1169. Defeated in Dublin, Ruaidrí kept hold of the Irish Midlands and retained his Connacht crown, inflicting several losses on the Normans. The O'Connor clan controlled Connacht until 1475, when the kingdom collapsed, and the dynasty subsequently divided into septs and became weakened by interfamily fighting.
The MacCarthys
Variations: Macarthy, McCarthy, McCarty
Irish name: Mac Cárthaigh
Meaning: Son of Cárthach
Parent dynasty: Eóganachta
Province: Munster
Founder: Cárthach mac Saorbhreathach
Historic seat of power: Blarney Castle, County Cork
The Mac Cárthaighs emerged from the Eóganacht Chaisil, part of a powerful dynasty that dominated Munster from 500 AD until the Dál gCais/O’Briens seized control of the province. The clan was formed from the flames of a fire deliberately set to kill the patriarch of the family, Carthach, in 1045.
The Mac Cárthaighs were forced from their fertile homeland (the Golden Vale that runs through Tipperary, Cork and Limerick) by the O'Briens, who’d emerged from the ranks of the Dál gCais and hugely expanded their powerbase under the leadership of Brian Boru, whose lifetime achievements and legacy following the 1014 Battle of Clontarf made them the most powerful force in Ireland.
The O'Briens' fortunes eventually ebbed, and Cormac Mac Cárthaigh (grandson of Carthach) became the last King of Munster before the province was divided into the kingdoms of Desmond and Thomond by the treaty of Glanmire in 1118. The O'Briens ruled Thomond, while Cormac's brother Tadhg Mac Carthaigh became King of Desmond, which covered most of the current counties of Cork and Kerry. The MacCarthys held power across most of Munster for the following 500 years.
There were four branches of the clan, with the MacCarthy Mór (the Great MacCarthy) sitting at the head, and the Duhallow MacCarthys, MacCarthy Reagh and MacCarthy Muskerry having their own areas of control. Blarney Castle in County Cork holds the famous Blarney Stone, apparently gifted to King Cormac Teige McCarthy by Robert the Bruce, King of Scots, as thanks for his support against the English in the 1314 Battle of Bannockburn.
The MacCarthys were pushed westward by the Normans (notably the FitzGeralds) and the Battle of Kinsale was fought and lost on what was once MacCarthy turf in 1601. Subsequently the Kingdom of Desmond was partitioned into Cork and Kerry, and the MacCarthys (who didn’t join the Flight of the Earls) got caught up in the conflict for the English crown fought between James II and William of Orange in the late 17th Century, after which they lost their titles and land.
The Kavanaghs
Variations: Cavanagh
Irish name: Caomhánach
Meaning: Belonging to Caomhán
Parent dynasty: Uí Ceinnselaig
Province: Leinster
Founder: Domhnall Caomhánach
Historic seat of power: Ballyloughan Castle, Carlow
The founder of this family group had good reason to start afresh, since his father, Diarmait Mac Murchada, is widely blamed for inviting the 12th-century Anglo-Norman invasion of Ireland by forming an alliance with Richard de Clare (Strongbow) in order to try and regain his position as King of Leinster, after being deposed in 1167 by the then-High King of Ireland, Ruaidrí mac Tairrdelbach Ua Conchobair (Rory O'Connor).
At the time, of course, Domhnall didn't know that his dad's decision would lead to 800 years of conflict, and he took his surname Caomhánach (later anglicised as Kavanagh) from St Caomhán Monastery in Wexford, where he grew up.
When Diarmait died in 1171, Domhnall was proclaimed King of Leinster by some clan chiefs, but sadly his father had promised Leinster (which included Dublin) to Strongbow as part of the dowry when offering his daughter Aoife (Domhnall's sister) in marriage to the Norman Nobleman. Inevitably, conflict ensued.
The Caomhánach clan retained control of a swathe of the province, with successive members of the family claiming the title King of Leinster and harassing Anglo-Norman stronghold of the Pale (an area around Dublin), along with the O'Toole and O'Byrne clans, right up until the early the 17th century, when the era of Gaelic royalty came to an end at the Battle of Kinsale.
