Æthelfrith (died c. 616) was King of Bernicia from c. 593 until c. 616; he was also, beginning c. 604, the first Bernician king to also rule Deira, to the south of Bernicia. Since Deira and Bernicia were the two basic components of what would later be defined as Northumbria, Æthelfrith can be considered, in historical terms, the first Northumbrian king. He was especially notable for his successes against the Britons and his victory over the Gaels of Dál Riata. Although he was defeated and killed in battle and replaced by a dynastic rival, his line was eventually restored to power in the 630s.