Also, there is no Megalomaniac ruling the world, pulling all our string and laughing at our inability to know or care who he or she is. Even if there was, why get rid of them? Happiness in Slavery, as I like to say.
No there is no one megalomaniac ruling the world. It's a class of wealth that makes up a very small minority of the population, and the emergence of that class and their coordination in maintaining themselves is an emergent behavior of the system as I see it.
Lets assume the planet starts from scratch. Every human being is given an equal chunk of the planet to call their own. Everyone has to trade whatever they have for whatever they don't have. Those who are ambitious and leverage their property more aggressively will accumulate more than those who are more content and generous. As they accumulate more, they will gain more leverage... snowballing the effect. Throw in successive generations of people who are born into the world without having been part of that original distribution of equal chunks. All they have to offer is themselves. Some property owners will make use of those people more aggressively than others, and continue to accumulate more and more. Over time, those who are greedy will consume those who are not. This upper class will continue to dwindle as it competes with itself, getting more and more vicious as it goes, but it will also cooperate to prevent competition arising from below. This isn't because humans are innately greedy or any such thing. It's because the system is designed to reward those who are greedy and turns into an environment which selects for such a disposition.
To relate this to the modern real world, take the state of politics in America. Two parties compete viciously with eachother, at least superficially, and between them they have the support of all major corporate interests. At the same time, those two parties work together to control the platform of political competition, as can be seen with the major televised political debates. The debates are funded and operated completely by the two major parties, and they hire security for the debates who are specifically instructed to threaten with arrest any third party candidate who even tries to come near the premises,
even carrying an invitiation. There is video out there of Nader confronting this situation outside of the 2008 debates, and I would link to it if I weren't at work.
And digging even deeper, there is a rich history of wealthy rivals cooperating to eliminate rising threats to their collective power, from strikebreakers during the industrial revolution to the dirty wars in South America.