what were usually supported by the middle class and replaced ruling aristocrats.

Question

This type of ruler took power by force and sometimes was very cruel, but some of them ruled very wisely.

Answer 1

This question is very general.  It may help if you put it in a specific context.  For example, prior to the French Revolution, France was ruled by the aristocracy.  After the revolution, the bourgeoisie emerged as the ruling class.  You can also argue that from antiquity through medieval and up to modern times, the trend has been

 

slavery → feudalism → aristocracy → capitalism.