Virgo Shaka was the Virgo Gold Saint of the XX century. He was born in a India and talked with Buddha since his childhood, becoming a Buddhist, learning his teaching. By Buddha (Shaka is supposedly the reincarnation of Buddha), Shaka discovery the eight sense, that allows live after death (the cosmo exist in the life, ergo, exist in a life after death), so, the death is only a new beginning; because this, Shaka is known as "the man who is almost a god".
Shaka is a Buddhist, but, in Saint Seiya universe, the characters have a own religion before become a Athena's (Hyoga is a christian) and continues with his religion. But, Shaka could feel the goodness in each person, and felt goodness in the pope (the pope self-proclaimed Athena's servant, ergo, Shaka follow the pope to serves Athena, and, feel by he, Athena's goodness). Shaka become a servant of the evil pope and was sent by a mission to kill the Black Saints (the Black Saints was villains too; the servants of pope have fought with Athena's enemies, because the pope only wished uncrown Athena and fight with her enemies during and after the process) but, Ikki ever had dominated them, and after a fight with Shaka, Shaka erase Ikki's memories, and, just seeing Shaka again, Ikki will recover the fear he felt in that fight.
Shaka continues with his "royallity" to Athena, and help the pope to brainwash Aiolia.
Ikki vs Shaka
Shaka, after defeat Shiryu, Shun and Seiya, fights again with Ikki. In anime, he sent your leaners to kill Ikki before (and help them with his cosmo), but Ikki defeats them and goes to the Virgo Temple.
Ikki loses your six senses in the fight with Shaka, but, uses the seventh sense to kill him; however, the impact only teleports Ikki and Shaka to another dimension, where Shaka could escape whenever he wanted. But, the Ikki opinions made Shaka became a neutral guy, and saves Ikki, waiting the battle end. Then, Shaka discovery that the pope is Gemini Saga, and swears loyalty to Athena.
Shaka is very arrogant, and thinks he deserves cult for his perfection and moral. He is not a neutral good hero, but a hater of the evil, and kill the evil with no piety and doubt, different of the other mistaken gold saints.
Shaka deprives his vision sense, to accumulate his cosmo and attack using it when his eyes are open. Ergo, Shaka is the saint with biggest cosmo, and can raise it quickly. He doesn't see anything with eyes when they are close, but uses another ways to see/feel the enemy.
Legend of Sanctuary
Shaka, in this movie, is not a declared Buddhist e is not a villain, but, a traitor of the pope and truly Athena servant (like Mu in the anime and manga, but, in this movie, he serves Athena before Mu). Unlike the Anime and Manga, Shaka helps Aiolia to escape of Saga's control (in a anime and manga, he helps Saga to brainwash Aiolia).