(Εὐθύδημος), an Athenian commander in the Peloponnesian war, was, at the close of its eighteenth year, B. C. 414, raised from a particular to a general command in the army besieging Syracuse. The object was to meet the urgent entreaty of Nicias for immediate relief from the burden of the sole superintendence, without making him wait for the arrival of the second armament. This position he appears to have occupied to the end, though probably subordinate as well to Demosthenes and Eurymedon as to Nicias. Whether he as well as his colleague Menander took part in the night attack on Epipolae appears doubtful. He is expressly named by Thucydides only once again, as united, in the last desperate engagement in the harbour, with Demosthenes and Menander in command of the ships. Diodorus names him in the previous sea-fight, as opposed on the left wing to the Syracusan Sicanus. Plutarch, who mentions his appointment with Menander, ascribes the occurrence of the second sea-fight, in which the Athenians received their first defeat, to the eagerness of the two new commanders to display their abilities. But this looks very like a late conjecture, such as Ephorus was fond of making, and is further inconsistent with the language of Thucydides, who represents the Syracusans as acting on the offensive, and shews in Nicias's letter that they had it in their power to force an engagement. Of his ultimate fate we are ignorant: his name (it is probably his) occurs as far back as the eighteenth year of the war, B. C. 422, among the signatures to the Lacedaemonan treaties. (Thuc. 5.19, 24, 7.16, 69; Diod. 13.13; Plut. Nicias, 100.20.)