Cleombrotus (Greek: Κλεόμβροτος): Spartan prince from the Agiad Dynasty, in 480/479 BCE regent of his nephew Pleistarchus.
King Anaxandridas of Sparta (r.c.560-c.520 BCE) had four sons: Cleomenes, Dorieus, Leonidas, and Cleombrotus, who may have been Leonidas' twin brother.note[Herodotus, Histories 5.41, 7.205, 8.71, 9.10.] Cleomenes succeeded his father in c.520 BCE and was king until his suicide in 488. At that moment, Dorieus had already died during an attempt to found a city on Sicily,note[Herodotus, Histories 5.43-47.] so Leonidas became king.note[Herodotus, Histories 7.205.] He was killed in action in the battle of Thermopylae, unable to prevent the Persian king Xerxes from invading central Greece (September 19, 480).note[Herodotus, Histories 7.223-225.]
Leonidas ought to have been succeeded by his son, Pleistarchus, but he was too young to become king, especially in war time. Therefore, Cleombrotus was appointed as regent. He commanded the Spartan forces in the weeks after the defeat at Thermopylae. While the Persians were looting Athens, he ordered the fortification of the Corinthian isthmus.note[Herodotus, Histories 8.71.] (The present wall, the Hexamilion, is a Byzantine reconstruction.)
On September 29, the united Greek navies defeated the Persians in the naval battle at Salamis, and Xerxes ordered his soldiers to retreat to Thessaly and Macedonia. Cleombrotus prepared a counterattack, but canceled it after a bad omen: a partial solar eclipse (October 2, 480).note[Herodotus, Histories 9.10.] He died in the following winter.note[Herodotus, Histories 9.10.]
Cleombrotus was the father of Pausanias, who succeeded him as regent and commanded the Greek forces during the battle of Plataea.note[Herodotus, Histories 9.10.] Another son was Nicomedes.note[Thucydides, Peloponnesian War 1.107.]