"Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men."
This arose as a quotation by John Emerich Edward Dalberg Acton, first Baron Acton (1834–1902). The historian and moralist, who was otherwise known simply as Lord Acton, expressed this opinion in a letter to Bishop Mandell Creighton in 1887
...From The Phrase Finder
It has always seemed to me that being a police officer would be a noble profession - I once considered it (as a child). Why then do some police become obsessed with their power?