The world is intertwined in ways that we can not begin to comprehend.  Only by analyzing every decision that every person ever made, could we even begin to justify some claim of understanding.  We tend to underestimate ourselves and the impact that each of us has on present and future society.  That is where social hierarchy's and classes originate in my opinion.  At some point in history, one group of people convinced another group that their influence was far greater.  It is when we accept these false notions influential capacity that we find ourselves trapped within a "class."  

Every choice we make alters the world.  It is the individuals who realize that power, who become our heroes, legends, saints, saviors, leaders, and villains. But even these people are nothing without those who follow them.

Considering that the human population of the world has been increasing exponentially since whenever it can be considered to have begun, it stands to reason that the most influential person must have lived during a time of extremely low human population, near the emergence of the species from the pregenitor stock. The further back in time you go, the more impact each individual has, because there are fewer individuals.

Logically, it seems most likely that the most influential individual must have lived before the population explosion that occurred about fifty thousand years ago. The best chances are for someone in East Africa at least two hunded thousand years before the New Kingdom of Egypt. That is if you include humans only and not pre-human hominids.

If you include pre-human hominids, it quickly becomes considerably more complicated, as you begin to rely even more on genetic causality than on basic middle-world causality.