14Duffy, Seán. Brian Boru and the Battle of Clontarf. Dublin: Gill & Macmillan, 2013. 11.
According to the author, Brian's family were "the Uí Thairdelbaig, who were a branch of the Déis Tuaiscirt, better known as Dal Cais, who were a branch of the Déis Bec, who were a branch of the Déisi of Munster."
The legendary founder of the Uí Néill dynesty, Niall Noígíallach, is depicted as striving to establish a strong, central monarchy in the 4th century CE, but was unable to do so. It was not until Brian Boru, six centuries later, that another effort was made to unite all the Irish tribes into a single alliance. According to Seán Duffy, "Níall may be more of a mythical figure than a historical one. Claims that the Uí Néill ruled Ireland from a very early period are hard to prove and may be a backward projection of later centuries. Certainly, no Uí Néill king could be proven to resemble anything like a king of Ireland until the middle of the ninth century." (Duffy, Seán. "Beal Boru and Magh Adhair on Voices from the Dawn." Message to the author. 1 May 2014. E-mail.)