He was the son of Heracles and the princess Auge, from Tegea. Auge's father, fearing an oracle that said his grandson would kill his uncles either, a) made the pregnant Auge a priestess of Athena and exposed the infant Telephus on Mt. Parthenion, who was then miraculously saved or suckled by a deer, and/or b) the infant Telephus and his mother were thrown into a crate and put into the sea where they landed in Asia Minor. The story of a child born under a curse and then exposed or set adrift and miraculously saved is common in Greek mythology, and in these respects Telephus differs hardly at all from Perseus, Oedipus, Romulus and Remus, or Heracles 1.
Telephus became king of the Mysians, where the Greeks mistakenly landed in their first attempt to find and besiege Troy. In the ensuing battle, Achilles wounded Telephus. When the wound would not heal, Telephus consulted an oracle which responded: "he that wounded shall heal."
In the reports we have about Euripides' lost play on the subject, Telephus went to Aulis disguised as a beggar to ask Achilles for help in healing his wound. Aristophanes has Aeschylus savagely criticize Euripides in his Frogs for having depicted a Greek hero so disgracefully. Achilles refused to heal the wound saying that he had no medical expertise. In another version of the story, Telephus is said to have somehow seized Orestes, the son of Agamemnon and leader of the Greeks, whom he threatened to kill unless Achilles agreed to help. But Odysseus pointed out that, as it was the spear that had inflicted the wound, the oracle meant that the spear must be the instrument of his healing. Scrapings from the spear were applied to Telephus' wound, and it was healed. This is another common motif in antiquity, the idea of sympathetic magic. In recompense Telephus was to lead the Greeks to Troy, but by this time Agamemnon had angered Artemis, and the Greeks were confined to Aulis.