Brian O'Neill of the Battle of Down ( K. of Ireland 1258 to 1260 ). He was the last Irish high king after nearly 1000 years of his dynasty. He smashed the rival MacLoughlin branch of the family at the Battle of cameirghe, where he killed his predecessor, King Domnall MacLoughlin, and ten men of his immediate family, thereby establishing O'Neill supremacy in the North of Ireland until the 15th century.
He became King of Ulster 1241 and formed a great Irish confederacy in 1256 to drive out the English. He was acknowledged as High King of Ireland 1258 and received willing hostages from O'Conor of Connaught, O'Melaghlin of Meath, and O'Brien of Thomond, but was killed 1260 by the mail-clad English at the decisive Battle of Downpatrick; his head was sent to London. He married Jill of Argyle, probably a daughter of Ducan Mac Dougall ( K. in the Hebrides and Lord of Lorn ) he left with other issue a son: Domnall K. of Ulster 1283 to 1286 and 1295 to 1325, Royal Heir of Ireland. He was deposed by the Red Earl of Ulster 1286, but restored 1295. He sent aid to Robert "the Bruce" in Scotland against the English 1316, and renounced his own right to the High Kingship in favor of Edward Bruce to save Ireland.
He headed the 22 dynasty's who adressed the Romstrance to Pope John XXII in 1317, and fought for Edward Bruce at the Battle of Dundalk 1318. He died 1325, leaving with other issue a son: Aedh Reamhar ( Hugh the Stout ) K. of Ulster 1344 to 1364. He deposed his kinsman Henry O'Neill, head of the senior Clannaboy branch from the High Kingship 1344, and invaded Clannaboy itself but was defeated 1345. He also levied tribute on the settlers in Louth. He married Gormfhlaith, probably a daughter of Aedh O'Donnell K. of Tír Conal. He left with other issue a son: Niall Mor ( the big or great ) was King of Ulster 1364 to 1394. He was opposed by his brother, Domnall who was an ally of the Clannaboy O'Neills; he defeated them and secured peace. He associated his son with him in the Kingship and died 1397, he married Beanmidhe daughter of his old enemy, Brian MacMahon. He left with other issue two sons:
(1) Henry Aimhreidh ( the Confused ) Royal heir of Cinel Eoghain about whom mant strange stories have been recorded, he married Affric daughter of Hugh O'Neill leaving with other issue a son:
Domnall ( K. of Ulster 1404 to 1432 ) He was captured 1399 by the English at the Battle of Dundalk and was sent to the Tower of London; he was ransomed 1401. He reign was a long struggle with his eventual successor, Eoghan O'Neill, who held him prisoner 1410 to 1414. He defeated the Mayor of Dublin 1423 and was killed 1432 in a skirmish with the O'Cahans.
(2) Niall Og " the young " ( K. of Ulster 1394 to 1403 ), styled Ua Néill Mor ( the great O'Neill ), which was the title used by this branch to distinguish them from their rivals of the Clannaboy branch, whose chief was styled " The O'Neill Buidhe. Froissart called him " le grand O'Nel " and described him as one of the four kings of ireland. He was knighed 1394 at Dublin by King Richard II of England. He married Una, daughter of Domnall O'Neill he died 1403, leaving with other issue a son:
Eoghan O'Neill ( K. of Ulster ), was crowned on the sacred stone at Tulach Og. He was opposed by Brian O'Neill, grandson of Henry Aimhreidh, whom he captured in 1435 with two of his sons and mutilated all three, cutting off one hand and one foot from each. He resigned the throne to his son Henry in 1455 and died 1456. He married Catairiona, daughter of Ardgal MacMahon ( K. of Oriel ) he had with other issue two sons:
(1) Henry O'Neill ( K. of Ulster ) whose son was Conn Mor King of Ulster, and his third son was Con Bacach " the Lame " King of Ulster and whose son was Shane the Proud ( Sean an Diomais ) (2) Aedh O'Neill ( Tanist of Cinel Eoghain ) He was surpised in 1434 by a force under Thomas Stanley ( K. of the Ilse of Man, Lord Lieutenant of Ireland ), but withdrew covered by his cavalry. He wounded Brian O'Neill in single mounted combat 1435, he died in 1475. His son: Art O'Neill ( K . of Ulster 1509 to 1514 ) had two sons. (1) Feidlimidh Ruadh O'Neill " the Red " ( Lord of the Fews ) (2) Niall Mor O'Neill who died 1538.