noun (n)

• a speaker who dictates to a secretary or a recording machine(noun.person)

  source: wordnet30
• a ruler who is unconstrained by law(noun.person)

  Synonym:
  potentate
  

  source: wordnet30
• a person who behaves in a tyrannical manner(noun.person)

  Example:
  My boss is a dictator who makes everyone work overtime.
  

  Synonym:
  authoritarian
  

  source: wordnet30
• One who dictates; one who prescribes rules and maxims authoritatively for the direction of others.(noun)

  source: webster1913