Jed Clampett. He’s good hearted, kind, and fair. Importantly, he also has a mojo working such that anything he attempts always works out for the best, even if he is operating with incorrect understanding of the situation.
I’d very happily follow the lead of President Josiah Bartlet (The West Wing), either Gandalf or King Elessar (LOTR), the unnamed President played by Henry Fonda (in Fail-Safe), Simon Kerslake (the selfless, dedicated British politician from Jeffrey Archer’s First Among Equals), Tolly Mune (the irascible but good-hearted planetary leader from George R.R. Martin’s Tuf Voyaging) or King Arthur.
But then again, I just wouldn’t want to live under a World Overlord. Better to have a Republic of Humanity with leaders we all elect, serving fixed terms. As Churchill said, “Democracy is the worst form of government, except for all the others that have been tried from time to time.”
Any of several extraordinarily upright and uncorruptible (and generally interchangeable) absolute leaders in the works of David Weber. Namely, Queen Elizabeth of the Star Kingdom of Manticore, or the king from Off Armageddon Reef, or the emperor from Hell’s Gate.
Let’s put Cobra Commander in charge! 
House is a superb doctor and would be a piss-poor world leader.
But lots of people wouldn’t, and he’s far too ethical to make them do so. Plus, running the X-Men is a very different job from running the whole world.
I have to agree with Vetinari. He’d be quite competent, and would focus on the good of the world above all else.
A few years back a bunch of Dopers voted for a guy named (omniously enough) Sauron as Emperor of the World.
Dang it, Algorithm, I came in thinking “No one will think of Tyrion Lannister!” But he’s perfect. People underestimate him, but he’s wickedly intelligent, plus fair and honest to a point. Ned Stark would not have made a good overlord. Too unbendable. But Tyrion’s a slippery little devil.
Quoth appleciders:
I would have guessed that Mr. Kobayashi meant the human Mycroft Holmes, Sherlock’s brother, not Mike AKA the HOLMES Mk. IV AKA Adam Selene AKA Simon Jester.
Another good option that I don’t think anyone has mentioned is Stephen Byerley. I agree with Dr. Calvin that he’s probably a robot, and also agree with her that that’s a good thing.
Yes, but I’d like him as leader because it would be hilarious, and comparatively make me look like less of an asshole.
Another vote for House, just for the inherent awesomeness of it all.
Imagine House with all the world’s power in his hands dealing with the Israel/Palestine situation or religious fanatics or jehova witness or mimes 
Good point. He did rise to world leadership and did a pretty damn good job at it, after all.
I love President Bartlett, but as Overlord?? Not so much.
I would rather have Michael Westen. He used to be a spy. He’s benevolent, and he knows intrigue!
Or Jules Winfield. A good authority figure since dodging the bullets. He could unite us. “English, Mother Fucker! You will speak it!”
Willy Wonka and his Oompa Loompa cabinet. Weapons of mass chocolate.
Rudi Mackenzie of S.M. Stirling’s Emberverse series, if he weren’t just too perfect. At any rate, he’s probably going to be some sort of emperor – the projected seventh volume is to be titled The High King of Montival.
How about Iznogoud? At least we’d know what we’re getting.
There is only one real choice: Mary Poppins
She is practically perfect in every way.
You’re overlooking his Mengele-style “experiments” on his workforce.
with Mark Antony as his designated successor?
That dumbass fucking stiff?! Hell, no! Let’s have Julius Caesar as depicted in Colleen McCullough’s “Masters of Rome” novels! That stud can do anything!
President Beck, as played by Morgan Freeman in Deep Impact, is all kinds of awesome: smart, modest, determined, reassuring. He’d have my vote for World Overlord, too.