The ancient Athenians considered themselves to be autochthonous, or indigenous people, claiming descent from the mythical first kings Cecrops and Cranaos. Cecrops, said to have been born of the earth with a serpent-like lower body, witnessed the famous contest between the deities Athena and Poseidon for patronage of the city. The god Poseidon claimed Athens by thrusting his trident into the middle of the Acropolis and producing a pool of salt water. Athena, instead, planted an olive tree at a spot to the west of the Erechtheion and this was judged by Cecrops to be the better gift.

The half-serpent Athenian ancestor and younger contemporary of Cecrops, Erichthonios, was born from the semen of Hephaestus, as it fell to earth during his attempt to violate Athena. She subsequently undertook to raise Erichthonios and when he came of age he replaced Cecrops as king of Athens. Erichthonios was thought to have erected the first cult statue of Athena on the Acropolis and instituted the annual Panathenaic festival. According to Homer, Athena installed Erichthonios' grandson, Erechtheus, in a temple dedicated to herself on the Acropolis, from which he later ruled Athens.

The legend of Theseus, his birth and ascent to the throne of Athens is one of the most important in Athenian mythology. Son of King Aegeus, he was a linear descendant of Erechtheus. On a visit to the city of Troezen, Aegeus took King Pittheus's daughter Aethra to bed and later, from this encounter she bore him a child, Theseus. Whwn he came of age, Theseus made his way to Athens taking with him sandals and a sword which would act as tokens by which Aegeus would recognize him as his son. After successfully defeating a number of dangerous brigands at the Isthmus of Corinth, Theseus attended a banquet given by father. Fearing him as a contender to the throne, Aegeus attempted to poison Theseus, but on seeing the sandals and sword realized his mistake and dashed the poisoned cup from his son's hands and embraced him as his successor.

Theseus was famous for slaying the half-bull, half-human creature, the Minotaur, that resided in the Cretan Labyrinth. King Minos of Crete had invaded Attica and Athens had agreed to pay tribute to him every year by sending seven youths and seven maidens to be devoured by the Minotaur. Theseus offered to go as one of the sacrificial youths in an attempt to slay the Minotaur. He told his father, Aegeus, that he would change the black sails of his ship to white if he succeeded. In Crete, Minos' daughter Ariadne advised Theseus to tie the end of a thread to the entrance of the labyrinth so he could retrace his path back from the center of the maze. Theseus succeeded in killing the Minotaur but forgot to change his ship's sails when returning to Athens. Spying his son's black-sailed ship, Aegeus in despair hurled himself into the sea, which has been known ever since as the Aegean.