KAUKON (or Caucon) was a priest of the goddess Demeter who established her Mysteries in the land of Messenia.

He was also the eponym of the Kaukonians, the people of the tiny region known as Triphylia, nestled between the lands of Elis, Arkadia and Messenia. The three genealogies applied to the figure of Kaukon no doubt derived from a long-running historical dispute over sovereignty of the region. As a son of Lykaon, Kaukon was an Arkadian, as a son Kelainos, a Messenian, and as a son of Astydameia, daughter of Phorbas, an Eleian.

Pseudo-Apollodorus, Bibliotheca 3. 8. 1 (trans. Frazer) (Greek mythographer C2nd A.D.) :
"Lykaon, reigning over the Arkadians, begat by many wives fifty sons, to wit . . . Kaukon . . ." [In a list of 50 sons, most of which are eponyms of places in the region. Kaukon was the eponym of Kaukonia.]

Pausanias, Description of Greece 4. 1. 5 - 9 (trans. Jones) (Greek travelogue C2nd A.D.) :
"The first rulers then in this country [of Messenia] were Polykaon, the son of Lelex, and Messene his wife. It was to her that Kaukon, the son of Kelainos, son of Phlyos, brought the rites of the Great Goddesses from Eleusis. Phlyos himself is said by the Athenians to have been the son of Ge (Earth), and the hymn of Musaios to Demeter made for the Lykomidai agrees.
But the mysteries of the Great Goddesses were raised to greater honor many years later than Kaukon by Lykos, the son of Pandion, an oak-wood, where he purified the celebrants, being still called Lykos' wood. That there is a wood in this land so called is stated by Rhianos the Cretan:--`By rugged Elaion above Lykos' wood.'
That this Lykos was the son of Pandion is made clear by the lines on the statue of Methapos, who made certain improvements in the mysteries. Methapos was an Athenian by birth, an expert in the mysteries and founder of all kinds of rites. It was he who . . . dedicated in the hut of the Lykomidai a statue with an inscription that amongst other things helps to confirm my account:–-`I sanctified houses of Hermes and paths of holy Demeter and Kore her firstborn, where they say that Messene established the feast of the Great Goddesses, taught by Kaukon, sprung from Phlyos' noble son. And I wondered that Lykos, son of Pandion, brought all the Attic rite to wise Andania.'
This inscription shows that Kaukon who came to Messene was a descendant of Phlyos, and proves my other statements with regard to Lykos, and that the mysteries were originally at Andania. And it seems natural to me that Messene should have established the mysteries where she and Polykaon lived, not anywhere else."

Pausanias, Description of Greece 5. 5. 5 - 6 :
"I have heard some who maintained that Lepreus was founded by Leprea, the daughter of Pyrgeus. Others say that the first dwellers in the land were afflicted with the disease leprosy, and that the city received its name from the misfortune of the inhabitants. The Lepreans told me that in their city once was a temple of Zeus Leukaios (Of the White Poplar), the grave of Lykourgos, son of Aleus, and the grave of Kaukon, over which was the figure of a man holding a lyre.
But as far as I could see they had no tomb of distinction, and no sanctuary of any deity save one of Demeter. Even this was built of unburnt brick, and contained no image."
[N.B. According to Aelian, below, Lepreus was sometimes described as the son of Kaukon.]

Pausanias, Description of Greece 4. 26. 3 - 27. 6 :
"[From the history of the liberation of Messenia from the Spartans :] A year before the victory of the Thebans at Leuktra [C4th B.C.], heaven foretold their return to Peloponnesos to the Messenians. It is said that in Messene on the Straits the priest of Herakles saw a vision in a dream . . . the dream indicated the recovery of Messene . . .
To Epaminondas [Theban general] it seemed in no way easy to found a city that could resist the Lakedaimonians, nor could he discover where in the land to build it. For the Messenians refused to settle again in Andania and Oikhalia, because their disasters had befallen them when they dwelt there. To Epaminondas in his difficulty it is said that an ancient man [i.e. the ghost of Kaukon], closely resembling a priest of Demeter, appeared in the night and said : `My gift to thee is that thou shalt conquer whomsoever thou dost assail; and when thou dost pass from men, Theban, I will cause thy name to be unforgotten and give thee glory. But do thou restore to the Messenians their fatherland and cities, for now the wrath of the Dioskouroi against them hath ceased.'
This he said to Epaminondas, and revealed this to Epiteles the son of Aiskhines, had been chosen by the Argives to be their general and to refound Messene. He was bidden by the dream, wherever he found yew and myrtle growing on Ithome, to dig between them and recover the old woman, for, shut in her brazen chamber, she was overcome and well-nigh fainting. When day dawned, Epiteles went to the appointed place, and as he dug, came upon a brazen urn.
He took it at once to Epaminondas [Theban general], told him the dream and bade him remove the lid and see what was within. Epaminondas, after sacrifice and prayer to the vision that had appeared, opened the urn and having opened it found some tin foil, very thin, rolled like a book. On it were inscribed the mysteries of the Great Goddesses, and this was the pledge deposited by Aristomenes. They say that the man who appeared to Epiteles and Epaminondas in their sleep was Kaukon, who came from Athens to Messene the daughter of Triopas at Andania.
When all was in readiness, victims being provided by the Arcadians, Epaminondas himself and the Thebans then sacrificed to Dionysos and Apollon Ismenios in the accustomed manner, the Argives to Argive Hera and Nemean Zeus, the Messenians to Zeus of Ithome and the Dioskouroi, and their priests to the Great Goddesses and Kaukon. And together they summoned heroes to return and dwell with them, first Messene the daughter of Triopas, after her Eurytos, Aphareus and his children, and of the sons of Herakles Kresphontes and Aipytos."

Aelian, Historical Miscellany 1. 24 (trans. Wilson) (Greek rhetorician C2nd to 3rd A.D.) :
"Kaukon son of Poseidon and Astydameia daughter of Phorbas had a child called Lepreus."
[N.B. Phorbas was a king of Elis.]

Sources:

• Apollodorus, The Library - Greek Mythography C2nd A.D.
• Pausanias, Description of Greece - Greek Travelogue C2nd A.D.
• Aelian, Historical Miscellany - Greek Rhetoric C2nd-3rd A.D.