Cleisthenes (also Clisthenes or Kleisthenes) was the tyrant of Sicyon from c. 600–570 BC, who aided in the First Sacred War against Kirrha that destroyed that city in 595 BC. He is also told to have organized with success a war against Argos because of his anti-Dorian feelings. After his victory he abolished all the rhapsodists of Homer, because they vaunted the citizens of Argos. The key innovation of his reign, which Herodotus mentions, is the reformation of the tribal system in the city of Sicyon. Herodotus states that he gave new names to all the tribes, calling his own non-Doric tribe, rulers of the people, and naming the other three Doric tribes after various animals. Herodotus does not however, relate exactly what Cleisthenes' reform was. Whatever this reform was, it must have been successful for all the tribes kept their names for a long time, even after the death of Cleisthenes.
Cleisthenes of Sicyon organized a competition with his beautiful daughter Agariste as the prize. The two main competitors for her were the Alcmaeonid Megacles, and Hippocleides. Because Hippocleides made a fool of himself by dancing drunkenly in front of Cleisthenes, Megacles was chosen to marry Agariste.
A relative of Cleisthenes was the later Cleisthenes of Athens and Agariste, the mother of Pericles.
His death is estimated around or before 532 BC.