Ailill is the first person awarded the title King of Leinster in the Annals of Ulster at his death notice since 838.
Francis John Byrne suggests that the root of this apparent confusion lay in the fact that the Uí Dúnlainge kings exercised little real authority due to the aggressions of their western neighbour Cerball mac Dúnlainge (died 888), King of Osraige.
[2] In 870 the high king Áed Findliath (died 879) invaded Leinster and overran it from Áth Cliath (Dublin) to Gabrán.
He reached Dún Bolg where his camp was attacked by the Laigin who were at first successful, but in a counter-attack they were put to flight.
Ailill's name is not connected with these events which state that Muiredach mac Brain was the King of Leinster who fought the forces of Cerball.