Cleisthenes (also Clisthenes or Kleisthenes) is the tyrant of Sicyon from c. 600–570 BCE, who aids in the First Sacred War against Kirrha that destroys that city in 595 BCE.

He is also told to have organized with success a war against Argos because of his anti-Dorian feelings.

After his victory he abolishes all the rhapsodists of Homer, because they vaunt 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.

His death is estimated around or before 532 BCE.