Saint Columba

On 9 June the church remembers Saint Columba, abbot, missionary, He is a patron saint of Scotland and Iona, and one of the three patron saints of Ireland, along with St. Patrick and St. Brigid. He is also revered as the patron of the city of Derry, Northern Ireland; poets; and bookbinders and is invoked against floods, 521 – 597.
But who was Columba? 
Saint Columba