Cassios was practically the first enemy of the series Saint Seiya. He was to Seiya who struggled to get his Pegasus Cloth. Apprentice Shaina, Cassios wanted the Pegasus Cloth, and with his height and musculature, thought would get to win the tournament with physical force that all saints have. He reached the final of the tournament after decapitates all challenges, and their final opponent would be Seiya, who as a child was always beaten by Cassios. Cassius decides to cut off the ear of Seiya, but Seiya cut his ear first. Seiya mocks Cassius for failing to develop Cosmo and so we always have the same physical strength; with the cosmos, Seiya overcomes the force of Cassios and defeat, leaving Shaina disappointed.
After the tournament
Cassios values his sensei, and loved to have made him a man. He (vowing revenge to Seiya) never forgave himself for losing the tournament to Seiya, which in its design, made his sensei lose morale. He went to live as a soldier of the sanctuary, because once there, could not get out unless one could Cloth. Aiolia later, still taking care of Cassius body.
After knowing that Shaina was injured trying to protect Seiya, he accepted defeat (he was the only ally of Shaina and had no connection with the Pope betrayed). Seiya invades the Leo Temple, and Cassios knew that Seiya would die if Shaina did not help him again in the fight against Aiolia, but he decided to protect Seiya he himself; thus, Shaina don't be sad about his death. Cassius commits suicide (hoping Aiolia leave the mental control of the Pope), but does not. Seiya hits Aiolia, and Aiolia turns back to the normal.