Cleon (ca. 475-422 B.C.) was an aggressive Athenian political leader. He was the first member of the nonaristocratic classes to reach a prominent position in Athens's political structure.
From humble origins, Cleon rose to prominence by attacking the Athenian strong man Pericles and endeavored to succeed him after 429. Exploiting the reaction against Pericles and the angry mood of the people during the Peloponnesian War with Sparta, Cleon advocated in 427 the execution of every adult male and enslavement of the rest of the population of Mytilene. A nominally free ally of Athens, the city had joined Sparta and had then been forced to capitulate to Athens. Cleon's policy was adopted at first but defeated by a small majority upon reconsideration. The news reached Mytilene just in time to stop the executions. Cleon's proposal to execute the ring-leaders—more than 1,000 according to the text of Thucydides—was carried out.
Thus Cleon identified himself with methods which more civilized Athenians, such as Thucydides and Aristophanes, regarded as savage and cruel. When Aristophanes denounced such methods in the comedy The Babylonians in 426, it was significant that Cleon prosecuted the producers of the play. Aristophanes retaliated in The Knights in 424, pinning on Cleon (whether justly or unjustly, it is not known) all the faults of the bullying demagogue and warmongering agitator.
Between the productions of these two plays, Cleon was very successful in the military field, though he had no experience of command. The opportunity had come in 425, when Athens had a temporary advantage in the war, having isolated a Spartan force on the island of Sphacteria near Pylos. Sparta offered peace and alliance on terms which Thucydides thought favorable. But Cleon persuaded the people to reject the offer. When this temporary advantage seemed to be slipping away, Cleon was criticized, but he turned the criticism against the generals at Pylos. One of them, Nicias, present in the Assembly, offered to resign when Cleon accused the generals at Pylos of incompetence for failing to capture the Spartans at nearby Sphacteria. The Assembly voted the command to Cleon, and with characteristic bluster Cleon said he would return within 20 days with the Spartans. With the help of Demosthenes, the general on the spot, Cleon succeeded.
Cleon now led the state in an aggressive policy, exacting more tribute from allies and attempting to regain lost territory. Sparta replied by opening a new front in Chalcidice, where allies of Athens defected. Cleon tried to deter them by making an example of the Thracian town of Scione. All adult males were executed and the women and children sold into slavery. But defections continued, and the Spartan commander, Brasidas, captured Amphipolis. In an attempt to redeem his prestige, Cleon obtained the command in this theater, was trapped by Brasidas, and perished with 600 Athenians in 422. Cleon's death cleared the way for an inconclusive peace.
Ancient sources for Cleon are Aristophanes, in The Knights, and Thucydides, both of them hostile. A useful modern study, which includes a discussion of Cleon, is H. D. Westlake, Individuals in Thucydides (1968). For background material, including a discussion of Cleon, see N. G. L. Hammond, A History of Greece to 322 B.C. (1959; 2d ed. 1967), and Charles A. Robinson, Athens in the Age of Pericles (1959).