Phormio (Greek: Φορμίων Phormion, gen.: Φορμίωνος), the son of Asopius, was an Athenian general and admiral before and during the Peloponnesian War. A talented naval commander, Phormio commanded at several famous Athenian victories in 428 BC, and was honoured after his death with a statue on the acropolis and a state funeral. He is considered the first great admiral in history.
Phormio first appears in the historical record in 440 BC, when he shared with Thucydides, Hagnon, and others the command of the Athenian fleet in the later part of the Samian War. In 432 BC, he commanded a force of 1600 hoplites sent to assist in the siege of Potidaea. Phormio led his men up slowly from the side of the city that the Athenians had not yet surrounded and constructed a counter-wall to complete Potidaea's investment. After Potidaea was firmly besieged, Phormio led his men in a successful campaign against Athens' enemies in the Chalcidice, and in the next year he again led an army attacking the Chalcidians, this time alongside Perdiccas II, king of Macedon.
In the winter of 429/8 BC, Phormio was sent out to the Corinthian Gulf as commander of a fleet of 20 triremes; establishing his base at Naupactus, Phormio instituted a blockade of Corinthian shipping. In the summer of 429 BC, however, Sparta began preparing a sizeable fleet and army to attack Athens' allies in the region, hoping to overrun Acarnania on land, capture the islands of Zacynthus and Cephallenia, and possibly even take Naupactus. Phormio was notified of these plans by the concerned Acarnanians, but was initially unwilling to leave Naupactus unprotected. When the Peloponnesian fleet began moving along the south shore of the Corinthian gulf, however, aiming to cross over to Acarnania, the Athenians followed along the north shore and attacked them once they passed out of the Gulf into the open sea and attempted to cross from the south to the north.