Favorite son of the humanities: My point was mainly that we shouldn't be so reductionist as to say that ideas are prime movers. They are formed in specific contexts. You said Princip was, essentially, a product of historical forces, or, to put it another way, his environment. I'm saying we should recognize that philosophers are too. I'm also not persuaded that common people are incapable of creating ideas. Social historians have written reams about concepts such as "moral economies" that have been at least as consequential in Western society as canonical "great ideas."
While I picked philsophers and religious thinkers in my response, the idea that it is "ludicrous" that common people can affect history is pretty much at odds with the past 40 years of historiography. People's actions may be shaped by larger forces, but post 33 seems to think that human agency plays little role in history. Further, in his zeal to discredit another perfectly legitimate argument, favorite son of the humanities also ignores a major contradiction in his own. If Gavrilo Princip can be dismissed as merely a product of larger historical forces, then so can Socrates. But ultimately, it does not diminish the genius of Socrates, Locke, Marx, or Mill to point out the obvious fact that their thought was influenced by underlying social factors. The ideologies that politics is "based on" were not formed in a vacuum.
So many great names mentioned in previous posts. I'm thinking Osama bin Laden. Not that he deserves kudos for his life and work, but if the criteria is that it in some way changed the world, I think one could make the argument that his leadership, organizational skills, resource management, and hate-mongering achieved a notorious end that was an international and political game-changer to say the least.
Sigmund Freud and Charles Darwin cannot be left off the list of top influential people who wrought change. With his analysis of dreams as a method to crack the human psyche, Freud was much ahead of his time. Also, his contention that repressed carnal desires in the psyche are responsible for much of the adults' actions was a monumental inroad in clinical psychology. His psychoanalytical theory of the Id, Ego, and Superego is one of the most influential theories of modern times.
Another extremely influential theory is modern times is that of Charles Darwin, whose theory of evolution and its basic mechanism, Natural selection, has greatly changed people's thinking about many issues in human behavior.
I agree with everything posted so far. But we should also look at people who changed the world for the worse. The two most obvious candidates for this are Hitler and Stalin, perpetrators of two of the worst mass killing sprees ever. They changed the way we think about the world we live in.
The above list is a great place to start. Those thinkers certainly changed the world intellectually, politically, and socially. We might also look to some scientists, engineers and inventors who have changed the world in more practical ways.
Thomas Edison helped change the world with electricity and the light bulb. Alexander Graham Bell helped with the telephone. Even Bill Gates helped to shape the world we live in with his work on personal computers.
I'll throw a few in in no particular order. Most of these stimulated religious, intellectual, or cultural change: