Elefenor, in Greek mythology, son of Calcodonand Alcione (according to Pseudo-Apolodorus) or Calcodon and Imonarete (according to other sources), was the king of Euboea during the Trojan War, to which he took forty ships.
His grandfather was Abas, son of Neptune and Aretusa, the first to reign in Euboea.
Abas had two sons with Aglaia, Calcodon and Canethus, and was killed, accidentally, by Elefenor, because the latter saw his grandfather being driven with a slave, who did not treat him with due care, and, in trying to hit the slave with a club, struck his grandfather, killing him. Elefenor was banished from Euboea after this event.
Calcodon, successor to his father Abas, defeated the Thebans, forcing them to pay an annual tribute, but was defeated by Amphiton, Heracles' human father. Calcodon and his wife Imonarete had two sons, Elefenor and Pyraechmes. Pyraechmes renewed war against Thebes, but was defeated and captured by Heracles, who executed him by tying him to horses and having him quartered.
Elefenor received the sons of Theseus, according to Pausanias, when Menesteus was placed as king of Athens by Castor and Pollux, or, according to Plutarch, when Theseus returned from the captivity of Molossia under Aidoneus and found the Athenians in rebellion against him.
He was one of Helen's suitors, to whom he offered various gifts.
Elefenor took Theseus' sons to the Trojan War as private citizens. He was killed in the Trojan War by Hector.