Adalgar was brother of the same name later Abbot of Corvey Adalgar; they came from a Saxon noble family. Like him, he first lived as a monk in the Benedictine monastery of Corvey on the Weser, where he met the Archbishop of Bremen and Hamburg, Rimbert. Adalgar Rimberts became assistant and followed him to Bremen. Adalgar was first coadjutor Rimberts and followed Rimbert after his death as Archbishop of Hamburg- Bremen to. Adalgar forced the missionary work in the north, but was hindered by the incursions of the Normans. Under his reign, the Archdiocese of Bremen was 895 at the imperial synod in Tribur degraded by Hermann of Cologne in an ordinary bishopric and placed under the direction of the Archdiocese of Cologne. He then sought the re- establishment of the Archdiocese, and was finally able to secure the independence of his diocese. Adalgar died on 9 May 909 in Bremen.
The feast day of St. Adalgar is 9 May ( date of death ). He is depicted in art as archbishop with pallium.