St. Oswin ruled as King of Deira (southern Northumbria) from 644-651, in the second generation after England's conversion to Christianity by St. Augustine of Canterbury. His father had been murdered by the warlord Cadwalla, and young Oswin had been spirited away to safety in Wessex shortly afterwards. Following the death of his kinsman, Oswald, at the hands of King Penda of Mercia in 642, he returned to Deira and became King around 644. His kinsman Oswy ruled Bernicia, the northern part of Northumbria.
Oswin had a great reputation for sanctity and justice, and for seven years the kingdom of Deira enjoyed great happiness and prosperity. But his kinsmen Oswy, jealous of his power, made war upon Oswin. Oswin found himself unable to best the armies of Oswy, and so he disbanded them and fled to the eorldorman Humwald of Gilling, whom had recently pledged allegiance to Oswin. But the unscrupulous Humwald quickly betrayed the saintly King Oswin to some of Oswy's officers who murdered him at Gilling in 651. The slain king was immediately venerated as a saint; Bede says of him, "He was most generous to all men and above all things humble; tall of stature and of graceful bearing, with pleasant manner and engaging address".
He was buried at Gilling, but his remains were lost during the Danish troubles . Only one year before the Norman Conquest (1065), St. Oswin appeared in a vision to a monk named Edmund and revealed the location of his body. On August 20th, 1103 his body was transferred solemnly to its final resting place. During the Dissolution of the Monasteries during Henry VIII's reign, his body was found to be intact in the tomb, but it was sacrilegiously destroyed. Only a fragment remained, which is now kept at Durham (above).
As a side note, Eanfleda, the wife of Oswin's murderer Oswy and daughter of St. Edwin, persuaded her husband to do penance for Oswin's murder by endowing a monastery at Gilling, which he promptly did. Some remains of the monastery can still be seen today, though it was destroyed by the Danes in the 11th century.