Okay kiddo, Gaetano Mosca was a smart guy from Italy a long time ago who studied how people act in groups and how they make rules for themselves.
He noticed that in every group, there are some people who are more powerful and others who are not as powerful. The more powerful people make the rules and control what happens in the group.
He also said that this is just the way things are and it's hard to change it. He called it the "iron law of oligarchy," which means that even in groups that claim to be democratic or fair, a small group of people will still have the most power and control.
Some people like his ideas and others don't, but Gaetano Mosca is remembered as one of the first sociologists to really study how groups work.