From the Catholic Encyclopedia:
An Irish monk who had studied under St. Senan, at Iniscathay (Scattery Island). He is placed as Bishop of Clogher by Ware and Lynch, but he resigned that see and became a monk at Iona about 630. His virtues, however, shone so resplendantly that he was selected (635) as first Bishop of Lindisfarne, and in time became apostle of Northumbria. St. Bede is lavish in praise of the episcopal rule of St. Aidan, and of his Irish co-workers in the ministry. Oswald, king of Northumbria, who had studied in Ireland, was a firm friend of St. Aidan, and did all he could for the Irish missioners until his sad death at Maserfield near Oswestry, 5 August, 642. St. Aidan died at Bamborough on the last day of August, 651, and his remains were borne to Lindisfarne. Bede tells us that “he was a pontiff inspired with a passionate love of virtue, but at the same time full of a surpassing mildness and gentleness.” His feast is celebrated 31 August.