Soos was a partially mythological king of Sparta

Sparta

Sparta or Lacedaemon, was a prominent city-state in ancient Greece, situated on the banks of the River Eurotas in Laconia, in south-eastern Peloponnese. It emerged as a political entity around the 10th century BC, when the invading Dorians subjugated the local, non-Dorian population. From c...

. According to Pausanias son of Procles

Procles

In Greek legend, Procles was one of the Heracleidae, a great-great-great-grandson of Heracles, and a son of Aristodemus and Argia. His twin was Eurysthenes. Together they received the land of Lacedaemon after Cresphontes, Temenus and Aristodemus defeated Tisamenus, the last Achaean king of the...

 and father of Eurypon

Eurypon

Eurypon, otherwise called Eurytion , son of Soos and grandson of Procles, was the third king of that house at Sparta, and thenceforward gave it the name of Eurypontidae....

. His name means stability a key concept for Spartan identity - such personifications of concepts are typical of orally transmitted lists. During his rule Spartans took away freedom of Helots

Helots

The helots: / Heílôtes) were an unfree population group that formed the main population of Laconia and the whole of Messenia . Their exact status was already disputed in antiquity: according to Critias, they were "especially slaves" whereas to Pollux, they occupied a status "between free men and...

, and took to themselves some territories of Arcadia

Arcadia

Arcadia is one of the regional units of Greece. It is part of the administrative region of Peloponnese. It is situated in the central and eastern part of the Peloponnese peninsula. It takes its name from the mythological character Arcas. In Greek mythology, it was the home of the god Pan...

.

Plutarch wrote that once Clitorians

Clitorians

Clitorians were the inhabitants of Kleitor in ancient Arcadia, made war with Spartan king Soos in 9 century BCE. They were mentioned by Plutarch, Pausanias, Xenophon. The Clitorians were members of Achaean League.-Description:...

encircled Spartans, preventing their access to water sources. Soos made an agreement that he would return lands if they would be allowed access to water. Then he promised the kingdom to the soldier who would not drink. Every one of them drank except Soos himself, so he refused to keep the agreement.