Answer
The Agiad dynasty, named after its founder Agis I, was the ruling dynasty of Sparta from its inception until the 5th century BCE. Leonidas I, the renowned Spartan king who led the defense of Thermopylae against the Persian invasion in 480 BCE, was a member of this dynasty. The Agiads shared power with the Eurypontid dynasty, with each dynasty providing one of Sparta's two kings.