According to ancient sources, he ruled Sparta in the 11th Century BC. His genealogy can be traced back first to the Eurysthenes, one of the legendary founders of Sparta, then all away to the Great Hero Heracles. Because of his legendary genealogy, he is rather a mythical figure exactly like Lycurgus.
According to ancient tradition, Agis I biggest achievements are the establishment of the port city of Patrai and the creation of the helots.
As we know a port city in the ancient world was vital for influence, economic power, and trade. Though a militarized society, the Spartans realized the importance of owning a port city.
Also, the conquest of the coastal settlement of Helos represented another great achievement of Agis I.
Unlike the establishment of Patrai, the citizens of Helos decided to rebel against the Spartan rule, but the revolt was quickly crushed. After the rebellion was crushed, the Spartans created the helots’ institution. From now on, the slaves from Helos would provide cheap labor and equipment for future wars of Sparta.
It is believed that starting with the rule of Agis I, the institution of dual kingship began in Sparta.
Regarding the creation of the dual kingship, modern-day historians consider that this settlement can be rather attributed to the fact that the Agiads had their base of power in the village of Pitana, and the Eurypontids in Limnai. Most probably the dual kingship was established when the villages of Pitana and Limnai decided to join their forces to form the polis of Sparta.