Put in GD rather than GQ because there’s not likely to be a straightforward answer. Which individual on the planet Earth has the highest overall influence, clout, power: the ability to have things his* way?
Back in the 1950s probably the most powerful single human alive was Josef Stalin: absolute dictator of a nuclear-armed totalitarian superpower. Every other dictator since looks like a pathetic El Supremo by comparison. For example Kim Jong-Il is very powerful in one small and ruinously poor nation, so his overall power on a global scale is significant but not tremendous.
It’s fashionable to refer to the President of the United States as the most powerful person in the world because of his role as leader of the preeminent nation on Earth. But while the POTUS has enormous responsibility, he is where he is only because a large number of influential people have supported his being there, and he is far from free to just do whatever he wants.
Lots of people are very rich, but in democracies even multi-billionaire status only goes so far. I doubt even Bill Gates could buy the right to kill people with impunity.
Some of the Arabian monarchs combine great wealth with great local power and geopolitical importance. Not too many people keep the king of Saudi Arabia waiting on hold. But is even their power largely derivative from the wealth and power of the West?
Who else then? Certain behind-the-scenes movers and shakers who shun the limelight but have the power to make or break administrations? Key players in the global economy? Who is pretty much acknowleged by those in the know as the king of the hill?
*presumably a male because women still face bigger disadvantages