Chapter XVIII of John Locke’s 2d Treatise on Government: Of Civil Government, “Of Tyranny,” discusses two marks of a tyrant: going beyond the law and working for their own (often unenlightened) self-interest rather than for the good of the people. John Locke says this several times in sections 199-202. I especially like this formulation:

… the difference betwixt a king and a tyrant to consist only in this, that one makes the laws the bounds of his power, and the good of the public, the end of his government; the other makes all give way to his own will and appetite.  

Drawing from sections 199-202, which you can see below, let me collect descriptors for a lawful ruler and a tyrant here:

Lawful Ruler(s):

• making use of power for the good of those who are under it

• commands and actions directed to the preservation of the properties of his people

• the law as the rule

• acknowledges himself to be ordained for the procuring of the wealth and property of his people

• bound to protect as well the people, as the laws of his kingdom

• glad to bound themselves within the limits of their laws

• makes the laws the bounds of his power, and the good of the public, the end of his government

• uses power for the preservation of the properties of the people

Tyrant(s):

• exercise of power beyond right

• making use of power for private separate advantage

• his will the rule

• commands and actions for the satisfaction of his own ambition, revenge, covetousness, or any other irregular passion.  

• thinks his kingdom and people are only ordained for satisfaction of his desires and unreasonable appetites

• makes all give way to his own will and appetite

• uses power to impoverish, harass, or subdue them to the arbitrary and irregular commands of those that have it

• transgresses law to another’s harm

• exceeds the power given him by the law, and makes use of the force he has under his command, to compass that upon the subject, which the law allows not

In section 202, John Locke argues that rulers bear a greater responsibility to obey the law and further the public good the more power they have. Great power does not absolve them of responsibility:

… the exceeding the bounds of authority is no more a right in a great, than in a petty officer; no more justifiable in a king than a constable; but is so much the worse in him, in that he has more trust put in him, has already a much greater share than the rest of his brethren, and is supposed, from the advantages of his education, employment, and counsellors, to be more knowing in the measures of right and wrong.

Below is the context for all of these points I have drawn out:

§. 199. AS usurpation is the exercise of power, which another hath a right to; so 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. When the governor, however intitled, makes not the law, but his will the rule; and his commands and actions are not directed to the preservation of the properties of his people, but the satisfaction of his own ambition, revenge, covetousness, or any other irregular passion.  

§. 200. If one can doubt this to be truth, or reason, because it comes from the obscure hand of a subject, I hope the authority of a king will make it pass with him. King James the First, in his speech to the parliament, 1603, tells them thus, “I will ever prefer the weal of the public, and of the whole commonwealth, in making of good laws and constitutions, to any particular and private ends of mine; thinking ever the wealth and weal of the commonwealth to be my greatest weal and worldly felicity; a point wherein a lawful king doth directly differ from a tyrant: for I do acknowledge that the special and greatest point of difference that is between a rightful king and an usurping tyrant, is this, that whereas the proud and ambitious tyrant doth think his kingdom and people are only ordained for satisfaction of his desires and unreasonable appetites, the righteous and just king doth by the contrary acknowledge himself to be ordained for the procuring of the wealth and property of his people.” And again, in his speech to the parliament, 1609, he hath these words, “The king binds himself by a double oath, to the observation of the fundamental laws of his kingdom; tacitly, as by being a king, and so bound to protect as well the people, as the laws of his kingdom; and expressly, by his oath at his coronation; so as every just king, in a settled kingdom, is bound to observe that paction to his people, by his laws, in framing his government agreeable thereunto, according to that paction which God made with Noah after the deluge. Hereafter, seed-time and harvest, and cold and heat, and summer and winter, and day and night, shall not cease while the earth remaineth. And therefore a king governing in a settled kingdom, leaves to be a king, and degenerates into a tyrant, as soon as he leaves off to rule according to his laws.” And a little after, “Therefore all kings that are not tyrants, or perjured, will be glad to bound themselves within the limits of their laws; and they that persuade them the contrary, are vipers, and pests both against them and the commonwealth.” Thus that learned king, who well understood the notion of things, makes the difference betwixt a king and a tyrant to consist only in this, that one makes the laws the bounds of his power, and the good of the public, the end of his government; the other makes all give way to his own will and appetite.  

§. 201. It is a mistake, to think this fault is proper only to monarchies: other forms of government are liable to it, as well as that: for wherever the power, that is put in any hands for the government of the people, and the preservation of their properties, is applied to other ends, and made use of to impoverish, harass, or subdue them to the arbitrary and irregular commands of those that have it; there it presently becomes tyranny, whether those that thus use it are one or many. Thus we read of the thirty tyrants at Athens, as well as one at Syracuse; and the intolerable dominion of the Decemviri at Rome was nothing better.  

§. 202. Wherever law ends, tyranny begins, if the law be transgressed to another’s harm; and him whosoever in authority exceeds the power given him by the law, and makes use of the force he has under his command, to compass that upon the subject, which the law allows not, ceases in that to be a magistrate; and, acting without authority, may be opposed, as any other man, who by force invades the right of another. This is acknowledged in subordinate magistrates. He that hath authority to seize my person in the street, may be opposed as a thief and a robber, if he endeavours to break into my house to execute a writ, notwithstanding that I know he has such a warrant, and such a legal authority, as will impower him to arrest me abroad. And why this should not hold in the highest, as well as in the most inferior magistrate, I would gladly be informed. Is it reasonable, that the eldest brother, because he has the greatest part of his father’s estate, should thereby have a right to take away any of his younger brothers’ portions? or that a rich man, who possessed a whole country, should from thence have a right to seize, when he pleased, the cottage and garden of his poor neighbour? The being rightfully possessed of great power and riches, exceedingly beyond the greatest part of the sons of Adam, is so far from being an excuse, much less a reason, for rapine and oppression, which the endamaging another without authority is, that it is a great aggravation of it: for the exceeding the bounds of authority is no more a right in a great, than in a petty officer; no more justifiable in a king than a constable; but is so much the worse in him, in that he has more trust put in him, has already a much greater share than the rest of his brethren, and is supposed, from the advantages of his education, employment, and counsellors, to be more knowing in the measures of right and wrong.

For links to other John Locke posts, see these John Locke aggregator posts: 

• John Locke's State of Nature and State of War

• On the Achilles Heel of John Locke's Second Treatise: Slavery and Land Ownership

• John Locke Against Natural Hierarchy

• John Locke's Argument for Limited Government