Autocracy
All power is in the hands of one person. Rule by a single all powerful authority A person or small group of people that maintain total control
It's called a dictatorship.
totalitarian authoritarian dictatorship
what type of government is demonstrated when one person or a small group holds sovereignty
Oligarchy is the rule of the few. In this system an elite group or even a single dictator has absolute power. This is always disastrous due to human nature.
They both are types of government, and both have a person/group of people who govern.
Authoritarianism
government
If by ruler you mean one person or a small group, then it would be called a "Dictatorship".
government
government
government