St Aidan’s Feast Day is 31st August in the Roman Catholic and Anglican calendars.
The following background is a precis of the Wikipedia article:
Saint Aidan of Lindisfarne, the Apostle of Northumbria (died 651), was the founder and first bishop of the Lindisfarne island monastery in England. He is credited with restoring Christianity to Northumbria. Aidan is the Anglicised form of the original Old Irish Aodhán, (meaning “little fiery one”).
An Irishman, possibly born in Connacht, Aidan was originally a monk at the monastery on the Island of Iona, founded by St Columba.
The Romans brought Christianity to Britain, but Anglo-Saxon paganism took over. Prince Oswald of Northumbria and his brothers lived among the Gaels of Dál Riata as princes in exile since their banishment by a rival royal house in 616 AD. Oswald may have visited the island monastery of Iona, and certainly converted to Christianity and was baptized. In 634 he regained the kingship of Northumbria, and determined to bring Christianity to the mostly pagan people there.
Owing to his Gaelic past, Oswald requested Irish missionaries from Iona, rather than the Roman-backed mission in southern England. The first bishop, named Cormán, met with no success and soon returned to Iona, reporting that the Northumbrians were too stubborn to be converted. Aidan criticised Cormán’s methods and was sent as a replacement in 635.
Aidan chose Lindisfarne, an island like Iona, close to the royal fortress of Bamburgh, as the seat of his diocese. King Oswald, who had a perfect command of Gaelic, often had to translate for Aidan and his monks, who spoke no English. When Oswald died in 642, King Oswine of Deira helped Aidan, and the two became close friends.
An inspired missionary, Aidan would walk between villages, politely conversing with the people he saw and slowly interesting them in Christianity. According to legend, the king gave Aidan a horse to save him walking, but Aidan gave the horse away to a beggar. By meeting people at their own level Aidan and his monks slowly brought Christianity to the Northumbrian communities. Aidan also took in twelve English boys to train at the monastery, to ensure that the area’s future religious leadership would be English.
In 651 a pagan army, led by Penda, attacked Bamburgh and attempted to set its walls ablaze. According to legend, Aidan prayed for the city, after which the winds turned and blew the smoke and fire toward the enemy, repulsing them; hence his patronage for fire fighters.
Aidan was a member of the Celtic branch of Christianity instead of the Latin branch, but his character and energy in missionary work won him the respect of Pope Honorius I and Felix of Dunwich.
Aidan’s friend Oswine of Deira was murdered in 651. Twelve days later Aidan died, on 31 August, in the 17th year of his episcopate, after falling ill.
The monastery he founded grew and helped found churches and other monasteries throughout the area. It also became a centre of learning and a storehouse of scholarly knowledge. Saint Bede the Venerable would later write Aidan’s biography and describe the miracles attributed to him. Aidan was also called the Apostle Of the English, unlike St Augustine who was merely the apostle of Kent.