Absolute Power Corrupts Absolutely

Origin

This is a quotation from Lord Acton, in a letter to Bishop Mandell Creighton, 1887:

"Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men."

Acton was preceded by William Pitt the Elder, who voiced a similar thought in a House of Lords speech in 1770:

"Unlimited power is apt to corrupt the minds of those who possess it; and this I know, my lords, that where laws end, tyranny begins."

Thoughts?

From the Phrase Finder: http://www.phrases.org.uk/meanings/22900.html