David Gemmell said this quote

There is a darkness in you. In all of us, probably. Beasts we keep chained. Ordinary men have to keep the chains strong, for if we let the beast loose then society will turn upon us with fiery vengeance. Kings though...well, who is there to turn upon them? So the chains are made of straw. It is the curse of kings, Helikaon, that they can become monsters. And they invariably do.