Chrysomallus was a fabulous, flying, golden-fleeced ram.
Athamas the Minyan, a founder of Halos in Thessaly but also king of the city of Orchomenus in Boeotia (a region of southeastern Greece), took as his first wife the cloud Nymph Nephele, by whom he had two children, the boy Phrixus and the girl Helle. Later he became enamored of and married Ino, the daughter of Cadmus, bringing drought upon his land when Nephele removed herself. Ino was jealous of her stepchildren and plotted their deaths: in some versions, she persuaded Athamas that sacrificing Phrixus was the only way to end the drought. Nephele, or her spirit, appeared to the children with a winged ram whose fleece was of gold. The ram had been sired by Poseidon in his primitive ram-form upon a nymph, Theophane, the granddaughter of Helios, the sun-Titan. Poseidon carried her away to an island where he made her into a ewe so that Theophane's other suitors could not distinguish the ram disguised god and his consort.
On the ram the children escaped over the sea, but Helle fell off and drowned in the strait now named after her, the Hellespont. The ram spoke to Phrixus, giving him heart, and took Phrixus, whose name means "curly"—as ram's fleece—safely on to Colchis, on the easternmost shore of the Euxine (Black) Sea. Phrixus then sacrificed the ram to Poseidon and settled in the house of King ally of Colchis and lived to a ripe old age. He hung the Golden Fleece reserved from the sacrifice on an oak in a grove sacred to Ares, where it was guarded by a dragon. There it remained until taken by Jason. The ram became the constellation Aries.
An unknown time after Jason had obtained the Golden Fleece it was taken and guarded by Polyphemus the Cyclops. He used it to make his island better, and to lure Satyrs there.
During The Mission to Cyclops Island. The Golden Fleece was recovered and used to heal the dieing tree that fuled the protective barrier around Camp Half-Blood. It accsdently revived the demigoddess Thalia Grace.