The Leo Cloth is the gold cloth of the Saint Aiolia (and briefly, Phoenix Ikki) in Saint Seiya, Regulus in Saint Seiya: The Lost Canvas and Kaiser in Saint Seiya: Next Dimension. It is the highest class of the cloths that Athena's Saints wear, the Gold Cloth.
The Leo Constellation was based on the Nemean Lion that Heracles faced as one of his legendary Twelve Labors. The creature's hide was impervious, so he had to trap it in its cave and strangle it to death, using its claws to skin it. While Heracles was allowed to keep his pelt, the lion's image found its place in the sky, as a constellation. Heracles wore this skin, considered it his armor including the lion's head as helmet, for the following battles. This was an inspiration to Kurumada for creating the warriors' Cloths and other armors in the series.
Leo Aiolia trained to be a Saint in Sanctuary, years before the birth of the modern Athena, by his brother, Sagittarius Aiolos *At least, according to the anime*. The cloth was likely kept in Sanctuary until a Saint worthy of wearing it was found. Aiolia was ordered to kill the Bronze Saints, but learned of Athena's place at their side and joined them. Gemini Saga used his "Phantom Demon Emperor Attack" to control Aiolia, and he fought Pegasus Seiya until Cassios killed himself to snap Aiolia out of it. Aiolia also fought off and killed many Specters during the Hades Arc. He was eventually trapped in Hell when trying to help the Bronze Saints get to Hades. He returned from being frozen in Cocytus, and combined his powers with the other Gold Saints to destroy the Wailing Wall, dying in the process. When it was sent to Elysion, by Poseidon, Phoenix Ikki donned the cloth, until Thanatos shattered it.
The Lost Canvas
Leo Regulus was the Guardian of the fifth house of Sanctuary in The Lost Canvas, and the youngest of the Gold Saints during that era. Regulus helped defend the ship that the Saints were going to repair to travel to The Lost Canvas, fighting off Behemoth Violate, and defeating her, but falling to Garuda Aiacos. While being defeated, he wasn't killed by Aiacos, just injured, as Sagittarius Sisyphus came to fight.
This is the form the Leo Gold Cloth takes on the manga. Aiolia earned the cloth in Sanctuary, and it was first seen when Aiolia arrived at the hospital to slay the rogue Bronze Saints. Like most Gold Cloth's original forms, it covers most of the body in a golden armor. The Cloth itself doesn't have any special abilities to differentiate itself from the other Gold Cloths. The Cloth was last seen in Hades, one of the five Gold Cloths send to Elyseum by Poseidon. Thanatos destroyed it and the other four Gold Cloths to show them that they weren't going to be saved by the Gold Cloths again.