Demetrius I or Demetrios I may refer to:Demetrius I of Macedon, king of Macedon Demetrius I of Bactria, Greco-Bactrian king Demetrius I Soter, ruler of the Hellenistic Seleucid Empire Pope Demetrius I of Alexandria, ruled in 189–232 Demetrius Zvonimir of Croatia, King of Croatia Demetrius I of Georgia, Georgian king Demetrios I Kantakouzenos, Despot of the Morea in 1383 Demetrius I Starshy, Duke of Bryansk Demetrius I Qadi (1861–1925), Patriarch of the Melkite Greek Catholic Church Demetrios I of Constantinople (1914–1991), Ecumenical Patriarch of Constantinople in 1972–1991