Tyrant
A tyrant (from Ancient Greek  τύραννος (túrannos) 'absolute ruler'), in the modern English usage of the word, 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, yet the word had a neutral connotation during the Archaic and early Classical periods. However, Greek philosopher Plato saw tyrannos as a negative word, and on account of the decisive influence of philosophy on politics,
Plato deemed tyranny the "fourth and worst disorder of a state." Tyrants lack "the very faculty that is the instrument of judgment"—reason. The tyrannical man is enslaved because the best part of him (reason) is enslaved, and likewise, the tyrannical state is enslaved, because it too lacks reason and order.  
The philosophers Plato and Aristotle defined a tyrant as a person who rules without law, using extreme and cruel methods against both his own people and others. The Encyclopédie defined the term as a usurper of sovereign power who makes "his subjects the victims of his passions and unjust desires, which he substitutes for laws".
In the late fifth and fourth centuries BC, a new kind of tyrant, one who had the support of the military, arose – specifically in Sicily.
One can apply accusations of tyranny to a variety of types of government:

to government by one individual (in an autocracy)
to government by a minority (in an oligarchy, tyranny of the minority)
to government by a majority (in a democracy, tyranny of the majority)

Etymology
The English noun tyrant appears in Middle English use, via Old French, from the 1290s.
The word derives from Latin tyrannus, meaning "illegitimate ruler", and this in turn from the Greek τύραννος tyrannos "monarch, ruler of a polis"; tyrannos in its turn has a Pre-Greek origin, perhaps from Lydian. The final -t arises in Old French by association with the present participles in -ant.

Definition
"The word 'tyranny' is used with many meanings, not only by the Greeks but throughout the tradition of the great books." The Oxford English Dictionary offers alternative definitions: a ruler, an illegitimate ruler (a usurper), an absolute ruler (despot), or an oppressive, unjust, or cruel ruler. The term is usually applied to vicious autocrats who rule their subjects by brutal methods. Oppression, injustice, and cruelty do not have standardized measurements or thresholds.

Greco-Roman culture
Ancient Greek and Sicilian tyrants were influential opportunists that came to power by securing the support of different factions of a deme. The word tyrannos, possibly pre-Greek, Pelasgian or eastern in origin, then carried no ethical censure; it simply referred to anyone, good or bad, who obtained executive power in a polis by unconventional means. Support for the tyrants could come from fellow oligarchs, from the growing middle class or from the peasants who had no land or were in debt to the wealthy landowners.
The Greek tyrants stayed in power by using mercenary soldiers from outside of their respective city-state. To mock tyranny, Thales wrote that the strangest thing to see is "an aged tyrant" meaning that tyrants do not have the public support to survive for long.

Archaic tyrants
One of the earliest known uses of the word tyrant (in Greek) was by the poet Archilochus, who lived three centuries before Plato, in reference to king Gyges of Lydia. The king's assumption of power was unconventional.
The heyday of the Archaic period tyrants came in the early 6th century BC, when Cleisthenes ruled Sicyon in the Peloponnesus and Polycrates ruled Samos. During this time, revolts overthrew many governments in the Aegean world. Chilon, the ambitious and capable ephor of Sparta, built a strong alliance among'st neighboring states by making common cause with these groups seeking to oppose unpopular tyrannical rule. By intervening against the tyrants of Sicyon, Corinth and Athens, Sparta thus came to assume Hellenic leadership prior to the Persian invasions. Simultaneously Persia first started making inroads into Greece, and many tyrants sought Persian help against popular forces seeking to remove them.

Corinth
Corinth hosted one of the earliest of Greek tyrants. In Corinth, growing wealth from colonial enterprises, and the wider horizons brought about by the export of wine and oil, together with the new experiences of the Eastern Mediterranean brought back by returning mercenary hoplites employed overseas created a new environment. Conditions were right for Cypselus to overthrow the aristocratic power of the dominant but unpopular clan of Bacchiadae. Clan members were killed, executed, driven out or exiled in 657 BC. Corinth prospered economically under his rule, and Cypselus managed to rule without a bodyguard. When he then bequeathed his position to his son, Periander, the tyranny proved less secure, and Periander required a retinue of mercenary soldiers personally loyal to him.
Nevertheless, under Cypselus and Periander, Corinth extended and tightened her control over her colonial enterprises, and exports of Corinthian pottery flourished. However, tyrants seldom succeeded in establishing an untroubled line of succession. Periander threw his pregnant wife downstairs (killing her), burnt his concubines alive, exiled his son, warred with his father-in-law and attempted to castrate 300 sons of his perceived enemies. He retained his position. Periander's successor was less fortunate and was expelled. Afterward, Corinth was ruled by a lackluster oligarchy, and was eventually eclipsed by the rising fortunes of Athens and Sparta.

Athens
Athens hosted its tyrants late in the Archaic period. In Athens, the inhabitants first gave the title of tyrant to Peisistratos (a relative of Solon, the Athenian lawgiver) who succeeded in 546 BC, after two failed attempts, to install himself as tyrant. Supported by the prosperity of the peasantry and landowning interests of the plain, which was prospering from the rise of olive oil exports, as well as his clients from Marathon, he managed to achieve authoritarian power. Through an ambitious program of public works, which included fostering the state cult of Athena; encouraging the creation of festivals; supporting the Panathenaic Games in which prizes were jars of olive oil; and supporting the Dionysia (ultimately leading to the development of Athenian drama), Peisistratus managed to maintain his personal popularity.
He was followed by his sons, and with the subsequent growth of Athenian democracy, the title "tyrant" took on its familiar negative connotations. The murder of Peisistratus' son, the tyrant Hipparchus by Aristogeiton and Harmodios in Athens in 514 BC marked the beginning of the so-called "cult of the tyrannicides" (i.e., of killers of tyrants). Contempt for tyranny characterised this cult movement. Despite financial help from Persia, in 510 the Peisistratids were expelled by a combination of intrigue, exile and Spartan arms. The anti-tyrannical attitude became especially prevalent in Athens after 508 BC, when Cleisthenes reformed the political system so that it resembled demokratia. Hippias (Peisistratus' other son) offered to rule the Greeks on behalf of the Persians and provided military advice to the Persians against the Greeks.The Thirty Tyrants whom the Spartans imposed on a defeated Attica in 404 BC would not be classified as tyrants in the usual sense and were in effect an oligarchy.

Sicilian tyrants
The best known Sicilian tyrants appeared long after the Archaic period. The tyrannies of Sicily came about due to similar causes, but here the threat of Carthaginian attack prolonged tyranny, facilitating the rise of military leaders with the people united behind them. Such Sicilian tyrants as Gelo, Hiero I, Dionysius the Elder, Dionysius the Younger, and Agathocles of Syracuse maintained lavish courts and became patrons of culture. The dangers threatening the lives of the Sicilian tyrants are highlighted in the moral tale of the "Sword of Damocles".

Later tyrants
Under the Macedonian hegemony in the 4th and 3rd century BC a new generation of tyrants rose in Greece, especially under the rule of king Antigonus II Gonatas, who installed his puppets in many cities of the Peloponnese. Examples were Cleon of Sicyon, Aristodemus of Megalopolis, Aristomachus I of Argos, Abantidas of Sicyon, Aristippus of Argos, Lydiadas of Megalopolis, Aristomachus II of Argos, and Xenon of Hermione.
Against these rulers, in 280 BC the democratic cities started to join forces in the Achaean League which was able to expand its influence even into Corinthia, Megaris, Argolis and Arcadia. From 251 BC under the leadership of Aratus of Sicyon, the Achaeans liberated many cities, in several cases by convincing the tyrants to step down, and when Aratus died in 213 BC, Hellas had been free of tyrants for more than 15 years. The last tyrant on the Greek mainland, Nabis of Sparta, was assassinated in 192 BC and after his death the Peloponnese was united as a confederation of stable democracies in the Achaean League.

Roman tyrants
Roman historians like Suetonius, Tacitus, Plutarch, and Josephus often spoke of "tyranny" in opposition to "liberty". Tyranny was associated with imperial rule and those rulers who usurped too much authority from the Roman Senate. Those who were advocates of "liberty" tended to be pro-Republic and pro-Senate. For instance, regarding Julius Caesar and his assassins, Suetonius wrote:

Therefore the plots which had previously been formed separately, often by groups of two or three, were united in a general conspiracy, since even the populace no longer were pleased with present conditions, but both secretly and openly rebelled at his tyranny and cried out for defenders of their liberty.
Citizens of the empire were circumspect in identifying tyrants. "...Cicero's head and hands [were] cut off and nailed to the rostrum of the Senate to remind everyone of the perils of speaking out against tyranny." There has since been a tendency to discuss tyranny in the abstract while limiting examples of tyrants to ancient Greek rulers. Philosophers have been more expressive than historians.
Josephus identified tyrants in Biblical history (in Antiquities of the Jews) including Nimrod, Moses, the Maccabees and Herod the Great. He also identified some later tyrants.

Greek political thought
The Greeks defined both usurpers and those inheriting rule from usurpers as tyrants. Polybius (~150 B.C.) indicated that eventually, any one-man rule (monarchy/executive) governing form would become corrupted into a tyranny.The Greek philosophers stressed the quality of rule rather than legitimacy or absolutism. "Both Plato and Aristotle speak of the king as a good monarch and the tyrant as a bad one. Both say that monarchy, or rule by a single man, is royal when it is for the welfare of the ruled and tyrannical when it serves only the interest of the ruler. Both make lawlessness – either a violation of existing laws or government by personal fiat without settled laws – a mark of tyranny."

In the classics
Tyranny is considered an important subject, one of the "Great Ideas" of Western thought. The classics contain many references to tyranny and its causes, effects, methods, practitioners, alternatives... They consider tyranny from historical, religious, ethical, political and fictional perspectives. "If any point in political theory is indisputable, it would seem to be that tyranny is the worst corruption of government – a vicious misuse of power and a violent abuse of human beings who are subject to it." While this may represent a consensus position among the classics, it is not unanimous – Thomas Hobbes dissented, claiming no objective distinction, such as being vicious or virtuous, existed among monarchs. "They that are discontented under monarchy, call it tyranny; and they that are displeased with aristocracy, call it oligarchy: so also, they which find themselves grieved under a democracy, call it anarchy..."The first part of Dante Alighieri's The Divine Comedy describes tyrants ("who laid hold on blood and plunder") in the seventh level of Hell, where they are submerged in boiling blood. These include Alexander the Great and Attila the Hun, and share the level with highway robbers.
Niccolò Machiavelli conflates all rule by a single person (whom he generally refers to as a "prince") with "tyranny", regardless of the legitimacy of that rule, in his Discourses on Livy. He also identifies liberty with republican regimes. Sometimes he calls leaders of republics "princes". He never uses the word in The Prince. He also does not share in the traditional view of tyranny, and in his Discourses he sometimes explicitly acts as an advisor to tyrants.Ancient Greeks, as well as the Roman Republicans, became generally quite wary of many people seeking to implement a popular coup. Shakespeare portrays the struggle of one such anti-tyrannical Roman, Marcus Junius Brutus, in his play Julius Caesar.
In Gibbon's Decline and Fall of the Roman Empire, Volume I, Chapter III, Augustus was shown to assume the power of a tyrant while sharing power with the reformed senate. "After a decent resistance, the crafty tyrant submitted to the orders of the senate; and consented to receive the government of the provinces, and the general command of the Roman armies..." Emperors "humbly professed themselves the accountable ministers of the senate, whose supreme decrees they dictated and obeyed." The Roman Empire "may be defined as an absolute monarchy disguised by the forms of a commonwealth." Roman emperors were deified. Gibbons called emperors tyrants and their rule tyranny. His definitions in the chapter were related to the absolutism of power alone – not oppression, injustice or cruelty. He ignored the appearance of shared rule.

Enlightenment
During the Age of Enlightenment, Western thinkers applied the word tyranny to the system of governance that had developed around aristocracy and monarchy. Specifically, English philosopher John Locke, as part of his argument against the "Divine Right of Kings" in his book Two Treatises of Government, defined it as such: "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." Locke's concept of tyranny influenced the writers of subsequent generations who developed the concept of tyranny as counterpoint to ideas of human rights and democracy. American statesman Thomas Jefferson described the actions of King George III as "tyrannical" in the United States Declaration of Independence.
Enlightenment philosophers seemed to define tyranny by its associated characteristics.
"The sovereign is called a tyrant who knows no laws but his caprice." Voltaire in a Philosophical Dictionary
"Where Law ends Tyranny begins." Locke in Two Treatises of GovernmentEdward Sexby's 1657 pamphlet, "Killing, No Murder" (PDF file) outlined 14 key traits of a tyrant, as the pamphlet was written to inspire the assassination of Oliver Cromwell, and show in what circumstances an assassination might be considered honorable. The full document mulls over and references points on the matter from early pre-Christian history, up into the 17th century when the pamphlet was writ. Of the most prevailing traits of tyranny outlined, "Killing, No Murder" emphasizes:

Prior military leadership service – tyrants are often former captains or generals, which allows them to assume a degree of honor, loyalty, and reputability regarding matters of state
Fraud over force – most tyrants are likely to manipulate their way into supreme power than force it militarily
Defamation and/or disbanding of formerly respectable persons, intellectuals, or institutions, and the discouragement of refined thinking or public involvement in state affairs
Absence or minimalization of collective input, bargaining, or debate (assemblies, conferences, etc.)
Amplification of military activity for the purposes of public distraction, raising new levies, or opening future business pathways
Tit-for-tat symbiosis in domestic relations: e.g. finding religious ideas permissible insofar as they are useful and flattering of the tyrant; finding aristocrats or the nobility laudable & honorable insofar as they are compliant with the will of the tyrant or in service of the tyrant, etc.
Pretenses toward inspiration from God
Pretenses toward a love of God and religion
Grow or maintain publish impoverishment as a way of removing the efficacy of the people's will[Original 1657 text:  https://archive.org/details/killingnomurderb00sexbuoft/page/n3/mode/2up]
In Scotland, Samuel Rutherford's Lex Rex and Alexander Shields' A Hind Let Loose were influential works of theology written in opposition to tyranny.
A modern tyrant might be defined by proven violation of international criminal law such as crimes against humanity.

Lists of tyrants
Lists include:

List of ancient Greek tyrants numbering several hundred plus those of Syracuse.
List of tyrants of Syracuse numbering about 20.
100 throughout history, including 40 from the 20th century
13 20th century tyrants
30 tyrants of the late 20th century
20 tyrants of the early 21st centuryThere are also numerous book titles which identify tyrants by name or circumstances.Among English rulers, several have been identified as tyrants by book title: John, King of England (who signed the Magna Carta), Henry VIII of England and Oliver Cromwell.

Methods of obtaining and retaining power
The path of a tyrant can appear easy and pleasant (for all but the aristocracy). A 20th-century historian said: Hence the road to power in Greece commercial cities was simple: to attack the aristocracy, defend the poor, and come to an understanding with the middle classes. Arrived at power, the dictator abolished debts, or confiscated large estates, taxed the rich to finance public works, or otherwise redistributed the over-concentrated wealth; and while attaching the masses to himself through such measures, he secured the support of the business community by promoting trade with state coinage and commercial treaties, and by raising the social prestige of the bourgeoisie. Forced to depend upon popularity instead of hereditary power, the dictatorships for the most part kept out of war, supported religion, maintained order, promoted morality, favored the higher status of women, encouraged the arts, and lavished revenues upon the beautification of their cities. And they did all these things, in many cases, while preserving the forms of popular government, so that even under despotism the people learned the ways of liberty. When the dictatorship [of the tyrant] had served to destroy the aristocracy the people destroyed the dictatorship; and only a few changes were needed to make democracy of freemen a reality as well as a form.
Ancient Greek philosophers (who were aristocrats) were far more critical in reporting the methods of tyrants. The justification for ousting a tyrant was absent from the historian's description but was central to the philosophers.

Obtaining
In the Republic, Plato stated: "The people have always some champion whom they set over them and nurse into greatness. [...] This and no other is the root from which a tyrant springs; when he first appears he is a protector".
Tyrants either inherit the position from a previous ruler, rise up the ranks in the military/party or seize power as entrepreneurs. Early texts called only the entrepreneurs tyrants, distinguishing them from "bad kings". Such tyrants may act as renters, rather than owners, of the state.
The political methods of obtaining power were occasionally supplemented by theater or force. Peisistratus of Athens blamed self-inflicted wounds on enemies to justify a bodyguard which he used to seize power. He later appeared with a woman dressed as a goddess to suggest divine sanction of his rule. The third time he used mercenaries to seize and retain power.

Retaining
Lengthy recommendations of methods were made to tyrants by Aristotle (in Politics for example) and Niccolò Machiavelli (in The Prince). These are, in general, force and fraud. They include hiring bodyguards, stirring up wars to smother dissent, purges, assassinations, and unwarranted searches and seizures. Aristotle suggested an alternative means of retaining power – ruling justly.The methods of tyrants to retain power include placating world opinion by staging rigged elections, using or threatening to use violence, and seeking popular support by appeals to patriotism and claims that conditions have improved.

See also
Big lie – Propaganda technique
Despotism – Government by a single entity with absolute power
Dictator – Political leader who possesses absolute power
Dictatorship – Form of government
List of ancient Greek tyrants
Outposts of tyranny – US foreign policy terminology used in the 2000s
Political repression
State terrorism
Tyrannicide – Killing of a tyrant or unjust ruler
Tyranny of the majority – Inherent oppressive potential of simple majority rule

References
External links

Tyrant by Jona Lendering at livius.org.
Loretana de Libero, Die archaische Tyrannis Bryn Mawr Classical Review
Victor Parker, A History of Greece, 1300 to 30 BC (chapter 7)