Demophilus led the Thespian contingent that stayed with Leonidas at Thermopylae.
Demophilus, son of Diadromes, commanded about 700 Thespian hoplites during the battle in 480 BC. When the main Greek force withdrew after the Persian army found a route around the pass, the Thespians chose to remain alongside Leonidas and the 300 Spartans. Herodotus presents their decision as voluntary: they refused to abandon the defenders who were preparing for a final stand.
The Thespians are sometimes overshadowed by the Spartans in popular retellings, but their sacrifice was substantial. Their contingent represented virtually the entire hoplite force Thespiae could field. Demophilus and his men fought and died at Thermopylae with the remaining defenders.
After the battle, Xerxes’ army burned Thespiae after its inhabitants had fled. The surviving Thespians later contributed troops to the Greek victory at Plataea in 479 BC. A common mistake is to identify Leonidas or another Spartan commander as leader of every Greek unit; Demophilus specifically commanded the Thespians.