25. Maximilien Robespierre
As the leader of the French Revolution, his regime was considered to be the regime of fear and it lasted for around 10 months. That was the period when mass murders were conducted, and he is supposed to be guilty for killing around 40, including King Louis XVI and Queen Marie Antoinette. He even guillotined the people who used to be his closest friends and declared that that is much better than forgiving them.
