Dionysius I

Dionysius I may refer to:

• Dionysius I of Syracuse (ca. 432–367 BC), Greek tyrant of Syracuse
• Dionysius I (Syriac Patriarch), or Dionysius Telmaharensis (died 845), Patriarch of the Syriac Orthodox Church
• Patriarch Dionysius I of Constantinople (died 1492), Patriarch of Constantinople
• Dionysius I, Metropolitan of Moscow (died 1385)
• Mar Dionysius I (died 1808), Metropolitan of the Malankara Church