Jacut was a 5th-century saint born in Wales to a royal family. As the son of Fragan, a prince of Dumnonia, he moved to Brittany with his parents to escape a plague in Cornwall. Raised in Ploufragan alongside his siblings, he eventually studied under Budoc of Dol on the Île Lavret. Throughout his adult life, he was active in the region, establishing several churches across Brittany.