Cleomenes or Kleomenes (died c. 489 BCE) was an Agiad King of Sparta in the late 6th and early 5th centuries BCE.

During his reign, which starts around 520 BCE, he pursues an adventurous and at times unscrupulous foreign policy aimed at crushing Argos and extending Sparta's influence both inside and outside the Peloponnese.

He is a brilliant tactician.

It is during his reign that the Peloponnesian League comes formally into existence.

During his reign, he intervenes twice successfully in Athenian affairs but keeps Sparta out of the Ionian Revolt.

He dies in prison in mysterious circumstances, with the Spartan authorities claiming his death was suicide due to insanity.