Its so hard to tell who is simply a product of changes in their times, and who is the changer of the time. For example, did Jesus spur the birth of Christianity, or was he simply the figurehead a group of Jews used to launch their own beliefs. Same goes for alot of scientists, were they the ones who actually changed the views of the world, or were they simply in the right place at the right time to discover something that would likely have been discovered very soon anyways. For example the people who developed the atomic bomb could be seen as signifigant in history, but if the US hadn't developed it in 1945 then someone whould have sooner rather than later. The scientific knowledge was all out there, it simply took the $$$ to develop them. The exact same designs were developed independantly be several groups.