Oswald was, according to Bede, 'most saintly and most victorious' and also 'most Christian'. The superlatives give a strong sense of the high regard in which Bede held the king who successfully introduced Christianity into Northumbria.
A son of the Bernician King Æthelfrith and his Deiran wife Acha, Oswald was born about 605. His childhood in the house of a successful warrior king was suddenly interrupted when he was about 11 years old and his father was killed in battle by the forces of King Rædwald of East Anglia supporting Edwin of Deira who then gained the throne. Northumbria under Edwin was no longer a safe place for the sons of Æthelfrith and so Oswald and his younger brother Oswiu fled north for safety in the Irish kingdom of Dal Riata in western Scotland. There they spent 18 years in exile. Eanfrith, their elder half-brother, fled to the kingdom of the Picts in Northern Scotland.
In 633 Edwin was overthrown and the kingdom overrun. Eadfrith returned as King of Bernicia but he was double-crossed and murdered by the invader Cadwallon. In the following year Oswald returned, drove out the invaders and became king in both parts of Northumbria. Bede presents the victorious Oswald as if he were a new Constantine. He describes how before the battle Oswald set up a cross at Heavenfield (near Hexham) and called on God's help for his just cause. During his exile, Oswald had converted to Christianity under the influence of the monastery of Iona and, according to one tradition, he attributed his victory over Cadwallon to the intervention of Iona's founder St. Columba. It is likely that he was assisted by Irish troops from Dal Riata in his army.
Once established in his kingdom, Oswald turned again to Iona asking the monastery to send someone to lead a mission to convert the Northumbrian people to Christianity. During Edwin's reign, the Italian bishop Paulinus had preached in Northumbria but much of what he achieved was lost when the kingdom was overrun and he himself fled south back to Kent. Oswald's arrangements were to prove more durable. After one false start, the Iona mission took root under the leadership of Bishop Aidan. The king endowed him with land to found a monastery on the island of Lindisfarne, not far from the royal centre at Bamburgh, and from there the mission spread throughout the kingdom. Oswald was actively engaged in promoting Christianity and the working partnership between bishop and king became the basis for a new form of governance in Northumbria. Bede shows Oswald putting himself in the service of the church by translating when Aidan, who at first spoke no English, preached at court. This humility on the king's part was matched by his excercise of the virtue of charity in his donations to the poor.
Oswald ruled directly in both Bernicia and Deira, though the devolved government of Deira in the first part of his successor Oswiu's reign suggests that the unity of Northumbria was not deep-rooted in the first half of the 7th century. Oswald did have a claim on the Deiran kingship through his mother Acha, but the violent deaths of the adult males of the Deiran house in the recent disturbances meant that he had no challengers.
His power extended more widely than his own kingdom: Bede says that he ruled over all the peoples of the British isles. This may be an exaggeration but we know little of the detail of the diplomacy or military force which Oswald deployed. He conquered the kingdom of Lindsey, just to the south of Deira and he exercised overlordship in the south of England in Wessex, Sussex and Kent. In Wessex he made a diplomatic alliance through marriage to Cyneburh and he acted as godfather to King Cynegils when he received baptism. We see in that episode how religious affiliation could be used as an element of diplomacy. Oswiu's marriage during this period to Rieinmelth suggests an alliance with the British kingdom of Rheged (in what is now north-west England) Oswald may have taken over the British kingdom of Goddodin after a siege at Edinburgh in 638. His dealings with the Irish of Dal Riata and the Picts are not clear.
Nor do we know how much authority Oswald exercised in Mercia, though this must have been the key to his English dealings. He can hardly have exercised over-kingship in the far south of England without secure passage through the midlands; and his wresting of Lindsey from the Mercian sphere of influence suggests a degree of control. In the end, however, Mercia was his undoing when he was defeated and killed in 642, in the thirty-eigth year of his life, by Penda of Mercia in alliance with the Welsh of Powys at the place Bede calls Maserfelth. This location is not known for certain but is generally thought to be in Mercian territory in the vicinity of Oswestry (in present-day Shropshire).
After his death, Oswald became the focus of a cult. His body was recovered from the battle field, where it had been dismembered, and his head was taken to Lindisfarne while his right arm was enshrined at Bamburgh. Bede gives accounts of miracles of healing associated with the place where his body was first lain and washed at the monastery of Bardney. In this way, the religious credentials of the Bernician dynasty were enhanced through their own in-house saint. These are aspects of a cult which was promoted officially; but there are also indications of a popular cult arising spontaneously at the site of Oswald's death. Cures were claimed for an injured horse and a girl suffering from paralysis, while a bag full of earth taken from the site miraculously survived a house fire.
In presenting Oswald as an epitome of a Christian king, Bede gives something of a one-sided account of his character. Edwin's widow Æthelburh who, even in Kent, was so fearful of Oswald that she removed her children to the protection of her kinsman the French king Dagobert and the monks of Bardney, who at first refused to receive his remains in the monastery, hint at a different perception: of the brutal qualities essential for a king in the raw power play of a vicious age.
