Dionysius I

• Dionysius I of Syracuse, Greek tyrant of Syracuse
• Dionysius I (Syriac Patriarch), or Dionysius Telmaharensis, Patriarch of the Syriac Orthodox Church
• Dionysius I, [Metropolitan of Moscow]
• Patriarch Dionysius I of Constantinople, Patriarch of Constantinople
• Mar Dionysius I, Metropolitan of the Malankara Church