He was of the Clann Faílbe sept of this branch and a grandson of Tnúthgal mac Donngaile (died 820), whom some sources name as King of Munster.
[1] His branch of the ruling dynasty had their lands in the Cashel area of Tipperary County.
The Fragmentary Annals record two defeats of the Norse Vikings by Munster groups in the year 852, though the dating is uncertain.
[3] After the death of Áilgenán in 853 there was an interregnum until the succession of his brother Máel Gualae mac Donngaile (died 859) in 856.
Áilgenán's great-grandson, Fer Gráid mac Clérig (died 961) was also a King of Munster.