Power is said to be the ability to control the action of other people around you.when can change the decision of other people using force or negotiations you are are said to powerful.some types of power include,
Physical power (the rock)
Political power (Joe Biden)
Economic power ( Alinko Dangote)
Expert power (Lionel Messi)
Referent power(Nelson Mandela)
Coercive power(Saddam Hussein) etc
Political power is said to be the ability to control people in a country without problem.but too much political power bring about dictators.
There is a popular saying that power corrupt, but absolute power corrupt absolutely.
It will only take a disciplined man to overcome the temptations of abusing power, must person feel when they have power they are on top of the world, they are above everybody, the truth is power doesn't corrupt anyone, just like money, power exposes the hidden character of an individual, a noble man is a noble man whether in power or not, a dictator is a dictator whether in power or not, .
Let me use your reference point as an example, Nelson Mandela was good whether in power or not he fought racial segregation in South Africa got arrested for 27 years and was even given power but despite all this he didn't abuse his office or misuse the power given to him, so power don't change people but rather brings out their true behaviour.