People

• Pope Leo I
  Pope Leo I
  Pope Leo I was pope from September 29, 440 to his death.He was an Italian aristocrat, and is the first pope of the Catholic Church to have been called "the Great". He is perhaps best known for having met Attila the Hun in 452, persuading him to turn back from his invasion of Italy...
  
   (400–461), also known as Pope Saint Leo the Great
• Leo I the Thracian, 5th century Byzantine Emperor
• 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

Other

• LEO (computer), first computer used for commercial business applications
• Leo I (dwarf galaxy)
  Leo I (dwarf galaxy)
  Leo I is a dwarf spheroidal galaxy in the constellation Leo. At about 820,000 light-years distant, it is a member of the Local Group of galaxies and is thought to be one of the most distant satellites of the Milky Way 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
  M96 Group
  The M96 Group is a group of galaxies in the constellation Leo. This group contains between 8 and 24 galaxies, including three Messier objects. The group is one of many groups that lies within the Virgo Supercluster The M96 Group (also known as the Leo I Group) is a group of galaxies in the...