Oswald, Saint, d. 641, king of Northumbria (633–41), son of Æthelfrith. In exile during the reign of Edwin, Oswald and his brother Oswy became Christians. After Edwin's death Oswald defeated (633) Cadwallon, king of North Wales, and recovered his father's kingdom. He brought from Iona a group of Scottish monks, led by St. Aidan, who established their base at Lindisfarne (see Holy Island) and introduced Celtic Christianity to Northumbria. Oswald was for a time the strongest ruler in England, being acknowledged overlord of Wessex and other southern kingdoms. Killed in battle by Penda of Mercia, he came to be revered as a Christian martyr. Feast: Aug. 5 in the Roman martyrology; Aug. 9 in Britain.