He appears in Greek mythology in connection with the story of the fight between Zeus and a monstrous son of Gaia and Tartarus called Typhoeus (Typhon). Typhoeus uses the very sickle that Zeus had been holding as a weapon to sever the sinews attaching Zeus' hands and feet to his body. He then hides them away until Hermes and Aigipan retrieve them.
Both Aigipan and Hermes are named as possible fathers of the god Pan, but Aigipan is also taken to mean the goat form of Pan, with Hermes as his father. Aigipan's parents may have been Zeus and a goat or Zeus and Aega (Aix), Pan's wife -- not necessarily any different from the first choice.
In "Cicero's Astronomy," Emma Gee (The Classical Quarterly, New Series, Vol. 51, No. 2 (2001), pp. 520-536) says that in Eratosthenes' Catasterismoi and the scholia on Aratus, Capricorn is Aegipan (Aigipan), the son of Pan and the she-goat Aix.
Ancient sources for Aigipan are Apollodorus, Plutarch, Hyginus, Oppian, and the Suidas, according to Theoi.
"When the gods in Egypt feared the monster Typhon, Pan bade them transform themselves into wild beasts the more easily to deceive him. Jove later killed him with a thunderbolt. By the will of the gods, since by his warning they had avoided Typhon’s violence, Pan was put among the number of the stars, Since at that time he had changed himself into a goat, he was called Aeocerus. We call him Capricorn."
(Theoi) Pseudo-Hyginus, Fabulae 196
