Eilean Mor appears in surviving documents as the Isle of St Finlagan (alternative spellings of the name being Findlugan or Fionn Lugain). A charter of 1427, for example, was witnessed as being granted "apud insula sancti Finlagani in Yle" (on the island of St Finlagan in Islay).
Findlugan was a contemporary of St Columba (who was born in 521). St Columba established an Abbey in Tamlaght near Lough Foyle in 585 and installed Findlugan as its first Abbot.
The monk made Scotland his missionary Field. Early monastic accounts tell how Findlugan saved the life of Columba when he interposed his body between the saint and a would-be assassin. This happened at Hinba, believed by some to have been Eileach an Naoimh, one of the Garvellochs, rocky islets north of Jura, or to have been Jura itself. It is possible Findlugan established an early monastic community on the island bearing his name. The Chapel built much later was certainly dedicated to him.
Over the years the spelling changed -the loch became known as Finlaggan and the island as Eilean Mor.