The Shadow Saint is a video game character, the totem of his armor is a skull and you face him at the end of the 12 Houses in the video game.
It first appeared in 1988, in the game for the Nintendo NES console “Saint Seiya Ougon Densetsu”. It was made during the Saga of the 12 Houses with some of the gold saints. The Patriarch would use the Armor of the Shadow Saint.
It’s a character conceived by the Japanese fan and design Ono gentleman was retouched by Masami Kurumada and was accepted for the game.