Erechtheus (; ) in Greek mythology was the name of an archaic king of Athens, the founder of the polis and, in his role as god, attached to Poseidon, as "Poseidon Erechtheus". The mythic Erechtheus and an historical Erechtheus were fused into one character in Euripides' lost tragedy Erechtheus (423/22 BCE). The name Erichthonius is carried by a son of Erechtheus, but Plutarch conflated the two names in the myth of the begetting of Erechtheus.