Dionysius was a 4th-century bishop who served as the Archbishop of Milan from 349 to 355. Likely of Greek origin, he maintained a friendship with the Roman Emperor Constantius II prior to his election. His tenure was defined by the intense theological conflicts between Arianism and the supporters of the Council of Nicaea. Due to his refusal to abandon the Nicaean faith during a synod in Milan, he faced exile alongside other religious leaders, eventually dying in Cappadocia.