thumb|King [[Jie of Xia holding a Ji polearm and sitting on two ladies.]]
thumb|Killing No Murder, cover page, 18th century reprint of 17th century English pamphlet written to inspire and [[Tyrannicide|make righteous the act of assassinating Oliver Cromwell]]
A tyrant () is an absolute ruler who is unrestrained by law, or one who has usurped a legitimate ruler's sovereignty. Often portrayed as cruel, tyrants may defend their positions by resorting to repressive means. The original Greek term meant an absolute sovereign who came to power without constitutional right, and the word had a neutral connotation during the Archaic and early Classical periods.
Ancient philosophers such as Plato and Aristotle saw tyrannos as a negative form of government, and on account of the decisive influence of philosophy on politics, deemed tyranny the "fourth and worst disorder of a state." They defined a tyrant as a person who rules without law, using extreme and cruel methods against both his own people and others. Plato in particular stated that: