Dacius was a 6th-century archbishop of Milan who served from approximately 530 until 552. Originally a monk, he became a prominent ecclesiastical politician and a staunch defender of Catholic orthodoxy during the Three-Chapter Controversy. He was a loyal ally to Pope Vigilius, resisting imperial pressure from Emperor Justinian I to accept certain theological edicts. His life was marked by the turmoil of the Gothic War, during which he sought Byzantine military aid for his city, and he eventually died in Constantinople.