Leonidas I was a 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 and Cadmus. Leonidas I was son of King Anaxandridas II. He succeeded his half-brother King Cleomenes I to the throne in c. 489 BC. His co-ruler was King Leotychidas. He was succeeded by his son, King Pleistarchus.
