John Locke as part of his argument against the "Divine Right of Kings" in his book Two Treatises of Government defines it this way: “Tyranny is the exercise of power beyond right, which nobody can have a right to; and this is making use of the power any one has in his hands, not for the good of those who are under it, but for his own private, separate advantage.” - http://en.wikipedia.org/wiki/Tyrant