Adalgar was a tenth-century archbishop who led the see of Bremen from 888 until his death in 909. Born around 900, he was the brother of the abbot of Corvey and originally served as a deacon alongside Rimbert. After being consecrated as a bishop to assist Rimbert, he eventually succeeded him as the third archbishop of the region. His leadership occurred during a period of significant political and ecclesiastical instability, which often limited his ability to carry out his missionary work.