Possible Clues:

• Napoleon's title (Abbr.)
• Hirohito's title (Abbr.)
• Ruler of anc. Rome
• Old Rom. ruler
• Napoleon or Nero: Abbr
• Ottoman, e.g.: Abbr.
• Old Mex. ruler
• Akihito, e.g.: Abbr.
• Charlemagne, for ex
• Hirohito's title: Abbr