Hippias was one of the sons of Pisistratus, and was tyrant of Athens in the 6th century BC.
Hippias succeeded Pisistratus in 527 BC, and in 525 BC he introduced a new system of coinage in Athens. His brother Hipparchus, who may have ruled jointly with him, was murdered by Harmodius and Aristogeiton (the Tyrannicides) in 514 BC. The Tyrannicides were executed by Hippias. After this, Hippias became a bitter and cruel ruler, and in 508 BC the Athenians decided to recall the Alcmaeonidae family, who had been exiled by Pisistratus. The Alcmaeonidae set about building a new temple at Delphi, then bribed the priestess to command the Spartans to help them overthrow Hippias. A Spartan force under Anchimolius was sent to help, but Hippias and his family, the Pisistratidae, allied with Cineas of Thessaly, and the Spartans and Alcmaeonidae were at first defeated. A second attempt, led by Cleomenes I of Sparta, successfully entered Athens and trapped Hippias on the Acropolis. They also took the Pisistratidae children hostage, and Hippias was forced to leave Athens in order to have them returned safely.
The Spartans later thought that a free, democratic Athens would be dangerous to Spartan power, and attempted to recall Hippias and reestablish the tyranny. Hippias had fled to Persia, and the Persians threatened to attack Athens if they did not accept Hippias; nevertheless the Athenians preferred to remain democratic despite the danger from Persia. Soon after this, the Ionian Revolt began. It was put down in 494 BC, but Darius I of Persia was intent on punishing Athens for their role in the revolt. In 490 BC Hippias, still in the service of the Persians, led Darius to Marathon, Greece. Accordng to Herodotus, Hippias had a dream that the Persians would be defeated, and they in fact were defeated at the Battle of Marathon.