Sparta was unusual among the Greek city-states in that it maintained its kingship past the Archaic age.
[4] The kings' firstborn sons, as heirs-apparent, were the only Spartan boys expressly exempt from the Agoge; however, they were allowed to take part if they so wished, and this endowed them with increased prestige when they ascended the throne.
Ancient Greeks named males after their fathers, producing a patronymic with the suffix -id-; for example, the sons of Atreus were the Atreids.
For royal houses, the patronymic was formed from the name of the founder or of an early significant figure of a dynasty.
If the descent was not known or was scantily known, the Greeks made a few standard assumptions based on their cultural ideology.
The Spartan kings as Heracleidae claimed descent from Heracles, who through his mother was descended from Perseus.