 He reputedly bore the nickname Sarffgadau, meaning battle-serpent.According to the Annals of Ulster and the Annals of Wales, in 616 he died at the Battle of Chester, fighting against Æthelfrith of Northumbria.The Annals of Ulster entitle him King of the Britons, perhaps because he led a combined force from more than one Brythonic kingdom at that battle against the Northumbrians.