It is commonly believed that Mac Cumhaigh was born in Creggan, County Armagh where a branch of the Uí Néill had been the traditional patrons of the poets under the old order.
His kindred, the Dáirine or Corcu Loígde, believed to be related to the Érainn, provided a number of powerful kings of Tara in the early period, and this could not be ignored by the Uí Néill compilers of the list.
Eugene O'Neill | Sam Neill | Martin O'Neill | Tip O'Neill | O'Neill | Gerard K. O'Neill | Peter O'Neill | Paul O'Neill | Hugh O'Neill, Earl of Tyrone | Uí Néill | O'Neill dynasty | Michael O'Neill | Jennifer O'Neill | O'Neill, Nebraska | Kevin O'Neill | John O'Neill | Hugh O'Neill | Susie O'Neill | Simon O'Neill | Seamus O'Neill | Felim O'Neill of Kinard | Ed O'Neill | Christopher O'Neill | Wedding of Princess Madeleine of Sweden and Christopher O'Neill | Tony O'Neill | Thomas P. O'Neill III | The Trials of Rosie O'Neill | Neill Calabro | Michael O'Neill (politician) | Laurence O'Neill |
Flaithbertach is first mentioned by the Irish annals in 907, when he is recorded, along with the then-King of Munster Cormac mac Cuilennáin, leading an expedition by the Munstermen against Connacht and the Uí Néill.
Máel Umai mac Báetáin (died c.608) was an Irish prince, the son of Báetán mac Muirchertaig of the northern Uí Néill, who appears to have been a significant figure in early Irish tales.
The remainder of the southern Uí Néill formed the kingdoms of Tethbae, in the north-west midlands, north and west of the River Inny and east of the River Shannon, and Brega in the east midlands, east of the upper part of the River Boyne and its tributary the River Blackwater.
The Annals of Ulster record that Cathal—usually taken to be Cathal mac Finguine, King of Munster—was first of all defeated by Domnall Midi and Clann Cholmáin Máir at Tailtiu, site of the main Uí Néill óenach, and then victorious against Fallomon and Clann Cholmáin Bicc at the Hill of Ward, site of the óenach of Tlachtga, second in importance only to that of Tailtiu.
The Horslips song "Dearg Doom", was itself based on the traditional Irish tune, O' Neill's March, (which appeared as Marcshlua Uí Néill on Sean O Riada's 1969 album "O'Riada sa Gaiety",) and which refers to Hugh O'Neill and his part in The Nine Year War.
He was killed in November 671 by Dub Dúin, king of Cenél Coirpri, a minor Uí Néill kingdom on the upper reaches of the River Boyne near Clonard.