Leo I may refer to:

• Pope Leo I (400–461), also known as Pope Saint Leo the Great
• Leo I (emperor), Roman emperor from 457 to 474
• Leo I, Prince of Armenia (d. 1140)
• Leo I, King of Armenia (1150–1219), sometimes also referred to as Leo II, or Levon I the Magnificent, first king of Cilician Armenia

• LEO (computer), first computer used for commercial business applications
• Leo I (dwarf galaxy), a dwarf galaxy that orbits the Milky Way Galaxy, and can be seen in the constellation of Leo
• The Leo I Group, a group of galaxies also known as the M96 Group

• Leo II (disambiguation)

This disambiguation page lists articles associated with the title Leo I.
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