The Romans were pretty good at that, as were the English. Anybody specific though, not sure…
There was also Napoleon, who held sway over his objectives, but not for very long.
I’m also really wanting to mention Vlad the Impaler, even though he wasn’t a conqueror. But it’s crazy to think that a small time ruler like him managed to fight off enemies with psychological warfare (when by all rights, their sheer numbers should have overwhelmed him) and keep the peace in his lands, even if it was through fear.
As for actual conquerors, I don’t know. Again, the Romans had Julius Caesar, who I guess was pretty badass in that respect.
Here’s a random list of top ten greatest rulers. (hitler wtf)