Xanthippus (/zænˈθɪpəs/; Greek: Ξάνθιππος, pronounced [ksán.tʰip.pos]; c. 525-475 BCE) was a wealthy Athenian politician and general during the early part of the 5th century BC. His name means "Yellow Horse." He was the son of Ariphron and father of Pericles. He is often associated with the Alcmaeonid clan. Although not born to the Alcmaeonidae, he married into the family when he wed Cleisthenes' niece Agariste, and would come to represent their interests in government. He distinguished himself in the Athenian political arena, championing the aristocratic party. His rivalry with led to his ostracism, only to be recalled from exile when the Persians invaded Greece. He distinguished himself during the Greco-Persian Wars making a significant contribution to the victory of the Greeks and the subsequent ascendancy of the Athenian Empire.
As a citizen-soldier of Athens and a member of the , Xanthippus most likely fought during the Battle of Marathon in 490 BCE. Xanthippus first appears in the historical record the following year (489 BCE), when he led the prosecution of Miltiades the Younger, the general who led Athenians to victory at Marathon. Miltiades had asked for a fleet of 70 ships and a supply of troops to be put at his disposal in reward for his victory, saying that he would not reveal his intentions, but that the venture would reap great profit for the city. The Athenians granted his wish, but when he met with set-backs and injury during an attack on Paros he had to return empty handed and sick. Many Athenians suspected him of deceiving them. The Alcmaeonidae were traditional political rivals of Miltiades' clan, the Philaidae, and they pressed for charges against the hero of Marathon, with Xanthippus making their case and asking for the death penalty. Miltiades was in great pain due to his injury and could not defend himself, but his friends put up enough of a defence to avoid his execution; instead he was fined a sum too large to pay and thrown in prison as a debtor. He died there of his wounds. Athenians would come to regret their treatment of their war hero, but immediately following the trial Xanthippus became the pre-eminent politician of the day, if only briefly.