Agis I (flourished 11th century bc?) was an early Spartan king, traditionally held to be the son of Eurysthenes (in legend, one of the twins who founded Sparta). Because the Agiad line of kings was named after him, Agis was perhaps a historical figure. The 4th-century-bc Greek historian Ephorus attributes to Agis the capture of the city of Helos in Laconia and the reduction of its people to helot (serf) status.