The 25 most ruthless leaders of all time

One man's hero is another man's tyrant, a popular aphorism goes.

But while we can argue the validity and virtue of certain political agendas, the callous methods by which some leaders attain their goals are less up to interpretation.

After all, no matter how a historian tries to spin it, ordering a tower to be constructed out of live men stacked and cemented together with bricks and mortar is pretty brutal.

Business Insider put together a list of the most ruthless leaders of all time featuring men and women who employed merciless tactics to achieve their political and military agendas.

Note: All people on the list ruled prior to 1980, and no living figures were included. People are arranged in chronological order.