His name is pronounced 'Oz-wee'. Oswiu was the brother of King Oswald of Northumbria. He became King after him. Oswiu was a warrior. He had led his brother's army which took over Gododdin (in Scotland). He got married lots of times. His first wife was the daughter of the King of North Rheged. So he inherited this kingdom. Oswiu spent most of his reign fighting against King Penda of Mercia. The Mercians took over Northumbria in AD 655. The two sides had a big battle. Penda's friends would not help him fight and he was killed. In AD 664, there was a big argument about when people should celebrate Easter. The Northumbrians worked it out the Irish way. A lot of people said you should do it the Roman way. Oswiu called a big meeting at Whitby to decide. The Roman Church won.