King of Sparta, ascended the throne B.C. 519. At the beginning of his reign he undertook an expedition against the Argives, defeated them, and destroyed a large number who had taken refuge in a sacred grove. He afterwards drove out the Pisistratidae from Athens.

This is the same Cleomenes whom Aristagoras endeavoured, but in vain, to involve in a war with the Persians.

He afterwards managed, by undue influence, to procure an oracular response from Delphi, pronouncing his colleague Demaratus illegitimate, and thus obtained his deposition. Becoming alarmed, subsequently, lest the fraud should be discovered, Cleomenes fled secretly to Thessaly, and from thence passing into Arcadia, he began to stir up the people of this latter country against Sparta. The Lacedaemonians, fearing his intrigues, recalled him, but he died soon after his return, in a fit of insanity, by his own hand (Herod. v. 64; v. 49 foll.; v. 65, etc.). (Harpers Dictionary of Classical Antiquities, 1898)