Ailill mac Fergusa
Ailill mac Fergusa was King of South Brega of the Uí Chernaig sept of Lagore of the Síl nÁedo Sláine branch of the southern Ui Neill. He was the son of Fergus mac Fogartaig and brother of Máel Dúin mac Fergusa, previous kings. he ruled from 797 to 800.
The annals record that he died from being thrown from a horse. He is styled rex Deisceirt Bregh-King of South Brega.