Leonidas I (; Doric Λεωνίδας, Leōnídas; Ionic and Attic Greek: Λεωνίδης, Leōnídēs [leɔːnídɛːs]; "son of the lion"; died 11 August 480 BC) was a warrior king of the Greek city-state of Sparta, and the 17th of the Agiad line; a dynasty which claimed descent from the mythological demigod Heracles. He was the husband of Gorgo, the daughter of Cleomenes I of Sparta. Leonidas had a notable participation in the Second Persian War, where he led the allied Greek forces to a last stand at the Battle of Thermopylae (480 BC) while attempting to defend the pass from the invading Persian army.