Æthelred I was King of the Bernicians from 745 to 748, and again from 749 to 762. The son and successor of King Earnwine , he came to power at a time when Bernicia was recovering from a long period of constant warfare against the neighbouring Britons, Picts and Scots. In the first years of his rule he fought the Picts of Fortriu who had ceased to pay tribute, with inconclusive results. In 747 he captured the fortress of Din Eidyn and relocated his capital there from Bebbanburh, thus alienating his English subjects as well as his British ones.
In 748 he was overthrown in a coup led by Oswiu, Ealdorman of Berewic, supported by a large number of English noblemen. Æthelred fled to his erstwhile enemies in Pictland, taking refuge with King Bridei V. The following year he invaded Bernicia at the head of a Pictish army, defeated Oswiu and reclaimed his throne.