The Golden Fleece comes to Colchis through Phrixus, who escapes sacrifice on the golden ram sent by Nephele. After reaching the kingdom of Aeetes, Phrixus sacrifices the ram and gives its fleece to the king. Later tradition places the shining hide on an oak in the sacred grove of Ares, where a great serpent watches it continuously. Pseudo-Apollodorus calls the guardian sleepless, and Apollonius makes its sharp eyes one of the defining dangers of Jason's quest.

The dragon's ancestry is not fixed. Apollonius describes it as a deathless and unsleeping offspring of Gaia, born on the slopes of the Caucasus near the rock associated with Typhon after the monster's blood falls upon the earth. Hyginus instead lists the Colchian dragon among the children of Typhon and Echidna. These are separate ancient genealogies and should not be blended into one parentage.

Pindar's Pythian Ode 4 gives one of the earliest surviving literary versions of the guardian. He says the dragon surpasses a ship of fifty oars in size, has glaring eyes and a speckled back, and is slain by Jason. The poem does not make Medea's drugging of the serpent the central solution, showing that Jason's direct victory belonged to an important early branch of the tradition.

Apollonius gives the dragon a different fate. When Jason and Medea approach the oak, the serpent sees them and raises its long neck with a hiss that echoes across the landscape. Medea invokes Sleep and uses powerful drugs until the creature's coils relax and its head sinks to the ground. Jason then takes the fleece while Medea remains beside the sleeping guardian. In this version the dragon is not killed, and the victory belongs primarily to Medea's knowledge rather than Jason's strength.

Pseudo-Apollodorus follows the drugging tradition. Diodorus preserves a more violent version in which Medea kills the serpent with poisons, while the Orphic Argonautica gives Orpheus a larger role in charming the guardian through song. The ancient tradition therefore offers several legitimate ways for the dragon to be overcome.

The dragon should not be confused with the source of the teeth Jason sows in Aeetes's field. In Apollonius and Pseudo-Apollodorus, Aeetes receives half of the teeth of the Theban dragon slain by Cadmus, with Athena preserving and distributing them. Those teeth produce the armed earth-born warriors Jason must defeat. Later retellings sometimes transfer the teeth to the Colchian guardian, but that is not the genealogy given in these principal surviving accounts.

Greek art preserves an even stranger image. A fifth-century BCE cup attributed to Douris shows the dragon apparently disgorging Jason while Athena stands nearby. No surviving literary narrative gives exactly that episode, so the image is evidence of an alternative visual tradition rather than proof of a standard written story. Whether slain, drugged, charmed or temporarily victorious, the Colchian Dragon remains the creature that makes the Golden Fleece impossible to take by ordinary means.