King of Northumbria (616-32)
He was the son and heir of Aella king of Deira, but was kept from his inheritance by Aethelfrith of Bernicia. Aethelfrith drove Edwin into exile and united the two kingdoms to form Northumbria.
When in exile Edwin certainly spent some time in Mercia where he married the daughter of king Cearl and tradition has him fostered by Cadfan ab Iago the king of Gwynedd. He eventually obtained the protection and support of Raedwald, king of East Anglia, and together they defeated and killed Aethelfrith at the battle of the river Idle in 617, which gave Edwin the rule of all Northumbria.
In 625 he remarried Aethelburh, daughter of Aethelberht king of Kent.
She bought with her the bishop Paulinus, and this seems to have led to the conversion of Edwin to Christianity and he was baptised at York with many of his followers.
Edwin wasn't content with Northumbria alone, he sought to expand the scope of his territories. In 617 he extinguished the Romano-British kingdom of Elfed and extended the reach of Northumbria westwards, over-running the kingdom of Gwynedd in north Wales (driving its ruler Cadwallon ap Cadfan into exile), and obtaining tribute from the Mevanian Islands(*). By which Edwin established his claim to being overlord or Braetwalda over the Anglo-Saxon kingdoms of Britain.
All this success naturally made Edwin a number of enemies, an assination attempt ordered by Cwichelm the West Saxon king almost succeeded in 626.
Edwin retaliated by invading Wessex where he,
felled on the spot five kings, and slew many of their men
according to the Anglo-Saxon Chronicle
He finally met his end when Cadwallon ap Cadfan returned from exile, allied himself with Penda of Mercia and invaded Northumbria in 632. Edwin was defeated and killed at the battle of Meigen or Hatfield Moor.
He was something of a hero to Bede, also a Northumbrian of course, who portrayed his reign as something of a golden age. But after his demise Northumbria fell into a state of collapse. His widow, together with Paulinus, fled back to Kent, his cousin Osric claimed Deira and Eanfrith son of Aethelfrith returned to seize Bernicia. It took the efforts of Oswald, another of Aethelfrith's sons, to reunite Northumbria.
(*) Believed on the basis of Bede
's description to be the islands of Man