There is no universally accepted ranking of
history's greatest rulers. The answer depends on the criteria used to evaluate their influence.

A comparative study might examine:
The political systems a ruler established or changed.
The longevity and stability of institutions.
Administrative and legal reforms.
Cultural, educational, or religious influence.
Military achievements and territorial expansion.
The human and social costs of their policies.
Cyrus the Great, Ashoka, Augustus, Charlemagne, Akbar, and Napoleon illustrate different dimensions of historical leadership. Comparing them within their own contexts produces a more thoughtful understanding than ranking them by conquest alone.
The Campus Review's guide introduces ten rulers whose legacies continue to attract historical interest.
https://thecampusreview.com/history-and-culture/greatest-rulers-in-history/