The Aries constellation was based on a flying golden ram, sent by the cloud goddess Nephele to rescue her son, Prince Phrixus, from being killed by his stepmother. When Phrixus reached the kingdom of Colchis, he sacrificed the ram to Zeus, and gave it as a present to the king of Colchis, Aeetes, who allowed Phrixus shelter in his kingdom. Aeetes hung the fleece in a sacred grove guarded by a dragon. This became the legendary Golden Fleece, which Jason and the Argonauts would later pursue.
Mu trained to be a Saint in Jamir years before the birth of the modern Athena by the previous wielder of the Aries Gold Cloth, Shion. The cloth was likely kept in Sanctuary until a Saint worthy of wearing it was found. Both Mu and Shion before him were capable of repairing Cloth. This doesn't seem to be a specific trait of the Cloth so much as passed on training. During Lost Canvas and Next Dimension, Shion is the Saint who receives the Aries Gold Cloth, and is a friend of the Libra Gold Saint. It is not revealed where Mu got his cloth, having had it since the beginning of the series, but Next Dimension reveiled that the previous Master of Sanctuary promoted Shion to a Gold Saint from a Bronze Saint just before Hades awakening. Mu was trapped in Hell along with Leo Aiolia and Scorpio Milo, but awakened by Athena's cosmo, and rejoined the Gold Saints, to add his power to theirs, at the cost of his life. Shion died by the betrayal of Gemini Saga, who killed him on Star Hill, and took his place.
Aries Shion and Libra Dohko, traveled together in Next Dimension, attempting to stop Hades from being reborn in the world, but failed due to the Pegasus Tenma stopping them. Their newly received Gold Cloths weren't enough, though, as the barrier weakened them as the Judges appeared. Shion learned via the Crateris Cloth that he is destined to be the future Master of Sanctuary.
This is the form the Aries Gold Cloth takes during the original Saint Seiya series. Mu earned the cloth in Jamir, and it was first seen when the Bronze Saints arrived at the first Gold Saint Temple during their assault on Sanctuary. Like most Gold Cloth's original forms, it covers most of the body in a golden armor. One of the special atributes in this Gold Cloth are those ram hornes making the owner so magestuos and at the same time simple, though the user does tend to have powerful techniques. The Cloth was last seen in Hades, not among the five Gold Cloths send to Elyseum by Poseidon.