A Spartan warrior, one of the Three Hundred sent to the Battle of Thermopylae. Along with a comrade, Eurytus, Aristodemus was stricken with an eye infection. King Leonidas ordered the two to return home before the battle, but Eurytus turned back, though blind, and met his end charging into the fray.

Herodotus believed (7.229-231) that had both Aristodemus and Eurytus returned alive, or had Aristodemus alone been ill and excused from combat, the Spartans would have ascribed no blame to Aristodemus. Because, however, Eurytus had turned back and died, Aristodemus was regarded as a coward and subjected to humiliation and disgrace at the hands of his compatriots. No Spartan would speak to him or give him a light to kindle his fire.

At the Battle of Plataea, Aristodemus fought with such fury that the Spartans regarded him as having redeemed himself. However, they would not award him any special prize for valor because he had fought with suicidal recklessness, and the Spartans regarded as more valorous those who fought while still wishing to live.

Another of the Three Hundred also survived Thermopylae. A man named Pantites, who had been sent by Leonidas on an embassy to Thessaly, failed to return to Thermopylae in time for the battle. Finding himself in disgrace in Sparta, he hanged himself.