For most of its history, the ancient Greek city-state of Sparta in the Peloponnese was ruled by kings. Sparta was unusual among the Greek city-states in that it maintained its kingship past the Archaic age. It was even more unusual in that it had two kings simultaneously, who were called the archagetai,^{[1][n 1]} coming from two separate lines. According to tradition, the two lines, the Agiads (Ἀγιάδαι, Agiadai) and Eurypontids (Εὐρυποντίδαι, Eurypontidai), were respectively descended from the twins Eurysthenes and Procles, the descendants of Heracles, who supposedly conquered Sparta two generations after the Trojan War. The dynasties themselves, however, were named after the twins' grandsons, the kings Agis I and Eurypon, respectively. The Agiad line was regarded as being senior to the Eurypontid line.^[3]

Although there are lists of the earlier purported Kings of Sparta, there is little evidence for the existence of any kings before the middle of the sixth century BC or so.

Spartan kings received a recurring posthumous hero cult like that of the similarly Doric kings of Cyrene.^[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. A ruling family might thus have a number of dynastic names; for example, Agis I named the Agiads, but he was a Heraclid and so were his descendants.

If the descent was not known or was scantily known, the Greeks made a few standard assumptions based on their cultural ideology. Agiad people were treated as a tribe, presumed to have descended from an ancestor bearing its name. He must have been a king, who founded a dynasty of his name. That mythologizing extended even to place names. They were presumed to have been named after kings and divinities. Kings often became divinities, in their religion.

The Spartan kings as Heracleidae claimed descent from Heracles, who through his mother was descended from Perseus. Disallowed the Peloponnesus, Hercules embarked on a life of wandering. The Heracleidae became ascendant in the Eurotas valley with the Dorians who, at least in legend, entered it during an invasion called the Return of the Heracleidae; driving out the Atreids and at least some of the Mycenaean population.

Years with no dates (only "c.") are unknown

The Achaean League annexed Sparta in 192 BC.