In 480 BCE, Dienekes was present outside the Temple of Apollo in Delphi when Leonidas met with the Cult of Kosmos accompanied by the Pythia. After Leonidas rejected the Cult's warnings in going to war with the King Xerxes I of Persia, whom the Cult supported, he instructed Dienekes to ready the Spartans for war.
Dienekes and the Spartans were stationed at a narrow passage in Malis blocking the road to mainland Greece. While Leonidas was observing the Persian fleet arriving from the cliff, Dienekes approached Leonidas, who was reminisced about how he would have liked to have gone fishing with his son. Dienekes later joined Leonidas and the rest of the Spartans in defending Malis against the Persian Empire, but ultimately perished in battle, having been stabbed in the neck.
By the 420s BCE, Dienekes' sacrifice at Thermopylae became legend. So much so that a play was written based on the battle. Written by Thespis, the part of Dienekes was set to be played by a nervous actor.