Oswiu (c. 612 15 February 670), also known as Oswy or Oswig (Old English: sw g), was a King of Bernicia. His father, Æthelfrith of Bernicia, was killed in battle, fighting against Rædwald, King of the East Angles and Edwin of Deira at the River Idle in 616. Along with his brothers and their supporters, Oswiu was then exiled until Edwin's death in 633. Following the death of his brother Oswald, defeated by Penda at the Battle of Maserfield on 5 August 642, Oswiu became King of the Bernicians. He passed the next decade in obscurity as one of many kings subject to Penda. In 655 Penda invaded Bernicia, driving Oswiu before him. The details of the campaign are unclear, but at the Battle of the Winwæd Oswiu unexpectedly defeated and killed Penda. This victory was followed by Oswiu's short-lived imperium he is traditionally counted as a Bretwalda over much of Great Britain.