Saint Columbanus (540 – 23 November 615; Irish: Columbán, meaning "the white dove") was an Irish missionary notable for founding a number of monasteries on the European continent from around 590 in the Frankish and Lombard kingdoms, most notably Luxeuil (in present-day France) and Bobbio (Italy), and stands as an exemplar of Irish missionary activity in early medieval Europe.
He spread among the Franks a Celtic monastic rule and Celtic penitential practices for those repenting of sins, which emphasized private confession to a priest, followed by penances levied by the priest in reparation for the sin. He is also one of the earliest identifiable Hiberno-Latin writers.
A description of him:
"By nature Columbanus was eager, passionate, and dauntless; these qualities were both the source of his power and the cause of his mistakes. The fascination of this complicated saintly personality drew numerous communities around him. Bobbio in Italy became a citadel of faith and learning, while Luxeuil in France became the nursery of saints and apostles. From the walls of Luxeuil went forth men who carried his rule, together with the Gospel, into France, Germany, Switzerland, and Italy."
If you want to read more about this great Irish missionary go here and here.