A government run by a dictator

Answer: Option B

One word substitute is Autocracy.

Democracy: a system of government by the whole population or all the eligible members of a state, typically through elected representatives.
Autocracy: a system of government by one person with absolute power.
Oligarchy: a small group of people having control of a country or organization.
Theocracy: a system of government in which priests rule in the name of God or a god.