Jim Lincoln wrote:
wikipedia on Lord Acton wrote:
Power tends to corrupt, and absolute power corrupts absolutely.

This is commonly referred to as Lord Acton's dictum. But it is the third phrase in this quote that might be the most important, if little-known:

Great men are almost always bad men.

Most people who quote Lord Acton's Dictum are unaware that it refers to Papal power and was made by a Catholic, albeit not an unquestioning one.