A ruler who governs with an iron fist, caring little for the welfare of the people, can be called despotic. Dictators and tyrants are often described as despotic.
Despotic is the adjective form of the noun despot, which means "tyrannical ruler." If you live under despotic rule, you probably have few rights and may fear your government. Use despotic to describe rulers that rely on brute force (or the threat of it) rather than the rule of law to keep order. Even if you're not the emperor of your own small kingdom, you might be a despotic boss, intimidating your employees. Might you consider switching to benevolence instead?