Starting around 550 B.C, the names become more familiar and there is some history about most of them. The famous Leonidas was of the Agiad line and, after he was killed at Thermopylae, his brother Cleombrotus served as regent for a year until his own son Pausanias was named the new Agiad king.
The Spartan kings had several major responsibilities, including acting as high priests for Spartan people and leading the army into battle. War was declared by the Assembly and the levy proclaimed by the Ephors, but the kings were the commanders. They also served on the Gerusia (council of elders) where their votes counted for two out of the thirty. Aristotle called the Spartan kingship a hereditary generalship but he was only half right. As hereditary leaders, the kings could wield great power over their peers who had to be elected.