Audoin (Ouen, sometimes 'Dado') was a noble Frank educated at the court of Chlothar II. He served as Referendary (head of chancery) to Dagobert I from 629 — overseeing all royal documents — with Eligius (the future saint) as a close colleague. In 641 he resigned secular office and was consecrated bishop of Rouen, governing the see for forty-three years.
He founded several monasteries — including Rebais and Jumièges — and was a great patron of monastic life in Normandy. He wrote the Vita of his close friend Eligius (after Eligius's death in 660), which is one of the most important biographical sources for the Merovingian period.
He died in 684 returning from a diplomatic mission to Cologne for King Theuderic III. His relics were translated to the great Abbey of Saint-Ouen at Rouen, the Gothic church that still bears his name and is one of the masterpieces of Norman flamboyant architecture.