Æthelfrith in the context of Oswiu

Edwin (Old English: Ēadwine; c. 586 – 12 October 632/633), also known as Eadwine or Æduinus, was the King of Deira and Bernicia – which later became known as Northumbria – from around 616 until his death. He was the second monarch to rule both of these northern English kingdoms and the first to convert to Christianity. After he died in battle, he was venerated as a saint.

Edwin was the son of Ælle, the first known king of Deira, and likely had at least two siblings. His sister Acha was married to Æthelfrith, king of neighbouring Bernicia. Edwin was forced into exile when Æthelfrith conquered Deira. His travels took him to the court of Rædwald of East Anglia, who defeated Æthelfrith in 616, allowing Edwin to ascend the thrones of Bernicia and Deira. After the death of his patron Rædwald around 624, Edwin became the most powerful ruler in Britain. Bede the Venerable includes him in his list of kings who exercised imperium over other Anglo-Saxon monarchs, and the Anglo-Saxon Chronicle gives him the title bretwalda, or "ruler of Britain".

Northumbria, a kingdom of Angles, in what is now northern England and south-east Scotland, was initially divided into two kingdoms: Bernicia and Deira. The two were first united by King Æthelfrith around the year 604, and except for occasional periods of division over the subsequent century, they remained so. The exceptions are during the brief period from 633 to 634, when Northumbria was plunged into chaos by the death of King Edwin in battle and the ruinous invasion of Cadwallon ap Cadfan, king of Gwynedd. The unity of the Northumbrian kingdoms was restored after Cadwallon's death in battle in 634.

Another exception is a period from about the year 644 to 664, when kings ruled individually over Deira. In 651, King Oswiu had Oswine of Deira killed and replaced by Œthelwald, but Œthelwald did not prove to be a loyal sub-king, allying with the Mercian King Penda; according to Bede, Œthelwald acted as Penda's guide during the latter's invasion of Northumbria but withdrew his forces when the Mercians met the Northumbrians at the Battle of Winwaed. After the Mercian defeat at Winwaed, Œthelwald lost power and Oswiu's own son, Alchfrith, became king in his place. In 670, Ælfwine, the brother of the childless king Ecgfrith, was made king of Deira; by this point the title may have been used primarily to designate an heir. Ælfwine was killed in battle against Mercia in 679, and there was not another separate king of Deira until the time of Norse rule.