Oswald (c. 604 - August 5, 642) was a King of Northumbria (634 - 642). He was the son of Æthelfrith of Bernicia, King of Northumbria.

After his father's death and defeat in battle against Raedwald of East Anglia, Oswald fled to Dalriada, where he was converted to Christianity by the monks of Iona. In 629, he fought under Connadd Cerr in the Battle of Fid Eoin in Ireland.

After the Welsh king Cadwallon ap Cadfan of Gwynedd, in alliance with Penda of Mercia, killed King Edwin in battle at Hatfield Chase in 633, Northumbria was split between its sub-kingdoms of Bernicia and Deira. Oswald's half-brother Eanfrith became king of Bernicia, but he was killed by Cadwallon in 634 after attempting to negotiate peace. Oswald then returned from exile with an army and marched against Cadwallon; his ranks were bolstered by Scots sent by the king of Dalriada, Domnal Brecc. The day before the two sides met in battle at Heavenfield, Oswald made his soldiers construct a wooden cross. He knelt down, holding the cross in position until enough earth had been thrown in the hole to make it stand firm. He then prayed and asked his army to join in. In the battle that followed, the Welsh were routed despite their superior numbers and pursued for miles by the Northumbrians; Cadwallon himself was killed.

Following this victory, Oswald reunited Northumbria. He is considered to have been Bretwalda in the years from 634 to 642, although his authority over the other Anglo-Saxon kingdoms seems to have been limited. He did, however, form an alliance with Wessex under Cynegils: Cynegils converted to Christianity and accepted baptism, and Oswald married Cyneburh, the daughter of Cynegils. With her he had a son, Æthelwald.

Although Edwin had previously converted to Christianity in 627, it was Oswald who did the most to spread the religion in Northumbria. It was he who gave the island of Lindisfarne to the bishop Aidan, who established a monastery there.

Oswald won some successes against the British to the north, but the primary concern of his reign was Northumbria's conflict with the rising power of Mercia under Penda. He was killed by the Mercians at the Battle of Maserfield in 642, and his body was dismembered by the pagan Penda. Oswald's head and limbs were placed on stakes, but according to legend, one of his arms was taken by his pet raven and dropped on a tree. The people quickly came to regard Oswald as a martyr and saint: a holy well of healing was said to have sprung up at the spot where the arm had landed, and the site soon became known as Oswestry, or "Oswald's Tree". His feast day is August 5.

Preceded by: Eanfrith	King of Bernicia	Succeeded by: Oswiu
Osric	King of Deira
Edwin of Northumbria	Bretwalda