"Power tends to corrupt, and absolute power corrupts absolutely."
- John Emerich Edward Dalberg Acton, first Baron Acton (1834–1902). The historian and moralist, otherwise known simply as Lord Acton, expressed this opinion in a letter to Bishop Mandell Creighton in 1887.
http://en.wikipedia.org/wiki/
John_Dalberg-Acton,_1st_Baron_Acton#cite_note-lmcone-3