John Dalberg-Acton, 1st Baron Acton said that
"[p]ower tends to corrupt, and absolute power corrupts absolutely."
What did he mean by this? How might power compel evil or restrict free will?
NOTE: This answer was given to a previous incarnation of this question. The block quotes I am responding to come from this incarnation. If I have the time I will modify my answer to respond more directly to this version of the question.
No, it isn't necessarily true, and that isn't a part of the claim Acton is making. Note the use of the word "tends". Many people have defended the possibility of a benevolent dictator. Plato's Republic advances an oligarchy of "Philosopher Kings", which he thought would produce the best society.
I don't think there is any very interesting connection between these two concepts, if anything it seems to be the opposite. Someone with absolute (unchallengeable) power would be faced with no external compulsions and so (assuming the possibility of free will) would have the best chance at freely acting.
NOTE: The following is a bit of an aside that is only indirectly relevant, but which you may, nevertheless, find interesting.
There is, however, an interesting claim that Socrates makes in Plato's Gorgias:
This weird claim has to do with Socrates' denial of akrasia, or weakness of will, where you act against what you believe to be best. Essentially, the claim he makes here is tyrants who commit evil are, in fact, slaves to their stupidity (to put it rather crudely). For, Socrates contends, they are making mistakes in measurement and wrongly considering the evil act to be the best.
This is, in fact, a bit of a caricature of the view, at least it doesn't explain it fully. I just thought it was interesting in connection with your question and presents a view on which "doing whatever you see fit" is not to have great power. It is also a view on which someone with the ability to do whatever they see fit actually does very little that they want to do.