In Greek mythology, Cepheus was a king of Tegea in Arcadia and a member of the Arcadian royal house descended from Pelasgus. He sailed with Jason and the Argonauts in the quest for the Golden Fleece, and is sometimes also listed among the hunters of the Calydonian boar. He later joined Heracles in the war against Hippocoon, king of Sparta, where he and his twenty sons fell in battle. He is distinct from the Aethiopian Cepheus, father of Andromeda.
Adapted from Wikipedia, "Cepheus (son of Aleus)" · CC BY-SA 4.0
I.Family
Cepheus was a member of the Arcadian royal family, the descendants of Pelasgus, the first king of Arcadia, and ruled at Tegea. He was usually identified as a son of Aleus, though the sources vary on his mother's identity.
According to Apollodorus, Aleus had, by Neaera the daughter of Pereus, a daughter Auge and two sons, Cepheus and Lycurgus. Hyginus instead names Cepheus the Argonaut as the son of Aleus and Cleobule. Some traditions made Cepheus a son of Lycurgus rather than of Aleus directly.
The Argonaut Amphidamas is counted as another brother of Cepheus and son of Aleus, though the sources disagree on the genealogy: Pausanias states that Aleus had three sons, Lycurgus, Amphidamas and Cepheus, while Apollodorus positions Amphidamas as a son of Lycurgus instead.
Cepheus had twenty sons, one of whom was named Aeropus, and several daughters. Among them was Sterope of Tegea, who figured in the story of his participation in the war against Hippocoon; Pausanias also names two further daughters, Aerope and Antinoe.
II.Mythology
In his youth, Cepheus joined Jason and the Argonauts in their quest for the Golden Fleece. He travelled with his brother Amphidamas and their nephew Ancaeus, the son of their brother Lycurgus.
Cepheus is also associated with the hunt for the Calydonian boar, though the relevant accounts list Ancaeus and Cepheus as sons of Lycurgus, reflecting the conflicting genealogical traditions about him; it remains uncertain whether this is the same Cepheus.
III.War against Hippocoon
When Heracles required assistance in his campaign against Hippocoon, king of Sparta, Cepheus was at first reluctant to join, fearing that Tegea would be left undefended and attacked in his absence.
To reassure him, Heracles gave Cepheus's daughter Sterope a lock of the hair of Medusa the Gorgon, which Athena had given him, with the instruction that holding it up three times from the city walls would put any attacker to flight. Thus convinced, Cepheus and his twenty sons joined Heracles's expedition.
Accounts of the outcome differ. According to Apollodorus, Cepheus and all of his twenty sons were killed in the battle, while Diodorus Siculus reports that all were killed except three of the sons.