Possible Clues:

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