What is a ruler who has absolute power over a country's government?

A dictator

E.g. Hitler was a dictator but was addressed as the fuhrer

Other titles used for designating absolute power can be king, queen, tyrant, Caesar, chairman, president, lord, and chief. It cannot be emphasized enough that some titles of those with absolute power can be disguised, such as the title of president....

Conversely, all people with absolute power, can in fact have this power "on paper" but in practice, absolute power is not always enforceable, as example der Fuhrer ordered certain German generals not to surrender and they did in fact do so. This happened in WW2 by German generals in Russia.

Also, the Emperor of Japan ordered all Japanese soldiers to fight to the death in Iwo Jima, and this order was disobeyed.