[Moderating]
There’s no factual answer possible for this. Moving to IMHO.
I’ll go the assassination route and say Gavrilo Princip or good old John Wilkes Booth.
It’s generally accepted that Genghis Khan killed enough people to allow the removal of 700 million tons of carbon dioxide from the atmosphere, roughly equivalent to the amount released in a year’s worth of gasoline demand. Well, not him personally, but the Mongols under his leadership.
Well, I got this PM once…
Would have been worth jackshit if that crazy woman hadn’t decided to bankroll him; he’d been kicked out of several courts already.
If we’re both thinking the same one. And I thought of that one before reading this post because he (? 
) popped up in my “friends” list when I logged in just now.
But back to the OP – I want to throw out a shout for Tanacharison (aka The Half King) for basically starting the first true World War in history by getting the English and French in North American (1753-54) shooting at each other. Especially for his role in the murder of Joseph Coulon de Jumonville. How greatly the War of Empire changed history and the fate of the world can be debated but like Princip its a little tougher to avoid the spark that started it.
I’d have to go with this.
Or back to Aristotle, for teaching us how to think.
Lots of fun suggestions.
I tend to perceive a difference between what I consider to be relatively discrete actions - such as Archipov’s “No” vote, an assassination, or my initial suggestion, as opposed to more prolonged processes like Borlaug’s ongoing research and advocacy or - I suppose - most inventions.
Yes, I imagine most ostensibly discrete actions can be interpreted as the result of prolonged processes, and most processes can be subdivided with an eye towards identifying specific turning points…
Gottfried Wilhelm Leibniz, who invented (discovered?) the binary code. Where would computers be without it? Where would people be without computers?
In that case I just have to suggest
:DHow about Louis Pasteur, who discovered germ transmission of diseases?
And teaching us so well that we were able, later, to prove most of his concrete ideas (e.g. physics) to be wrong.
I vote for the person who invented 0. Some Sumerian, perhaps? And some Mayan, independently…
Guy who lived about the turn of the first century. Name was Jesus. They killed him, but he live on.
St. John Philby was the father of Kim Philby, the spy. He was an Arabophile and became part of the court in Saudi Arabia. He had anti british sentiments for his whole life.
It was under his direct influence that it was decided to award the oil franchise for the country to standard oil of New Jersey as opposed to British Petroleum. That was the biggest business contract in history, and it made for a very different world.
Naw - the influential person was whoever thought to hide the body!
Without Thomas Edison we would have to watch TV in the dark.
I would discount most inventions and scientific discoveries because they just shift the timeline.
Slight hijack, but I was thinking about this earlier. Austro-Hungarian Chief of Staff Conrad von Hötzendorf tried a number of times to get Emperor Franz Joseph to go to war with Serbia. His chief opponent was Franz Ferdinand. Gavrilo Pricip assassinated the one person who could have stopped the war from beginning as it did. Talk about an own-goal.
I know you and others have mentioned assassins.
I think Gavrilo Princip assassinating Archduke Franz Ferdinand had more far reaching effects than any other assassin metioned so far. It triggered a chain of events that ended up provoking two world wars.
Abraham Lincoln’s and JFK’s assassinations were tragic events but I really don’t see them having any far reaching consequences that still affect the world as much as Archduke Ferdinand’s death did.
Another vote for Columbus. Sure, he had a crew and received financing from the Spanish government. But he was individually the driving force for sending a western expedition across the Atlantic. And the impact of linking the Old World to the New World was enormous.
Booth I threw in because I am not all that impressed with Lincoln as a President in general terms but I have little doubt our national history would have been very different if he had survived his second term. And with those possible differences maybe, just maybe, more could have been effected than we know.