Cassios is a prominent character within the narrative of the original anime series Knights of the Zodiac, known as a formidable aspiring knight from the Sanctuary. His role is deeply tied to themes of unrequited love, bitter rivalry, and eventual redemption through self-sacrifice.

In terms of background, Cassios is a Greek native who trained for six years under the严厉 tutelage of Shaina, the Silver Saint of Ophiuchus, with the specific goal of claiming the Bronze Cloth of Pegasus. Physically imposing, he stands at an exceptional height with a muscular build, bronze skin, white hair styled in a short mohawk, and sharp, pale eyes. A defining physical characteristic acquired during his life is the loss of his left ear, a wound he suffered in combat.

Cassios possesses a personality that contrasts sharply with his brutish and intimidating appearance. While he displays aggression and a savage brutality in combat, even reportedly decapitating fallen opponents, he also harbors a surprisingly large and noble heart. His driving motivation is his deep, consuming love for his master, Shaina. This love is the cornerstone of his actions, fueling his initial desire to win the Pegasus Cloth to honor her and later guiding his most pivotal decisions.

His primary role in the story is that of an initial rival and antagonist to the protagonist, Seiya of Pegasus. He and Seiya become the final contenders in a tournament held at the Sanctuary to determine the rightful owner of the Pegasus Bronze Cloth. Confident in his immense physical strength, Cassios believes the Cloth is his birthright as a Greek and looks down on the Japanese Seiya. During their final match, Cassios dominates early on using his raw power and attempts to sadistically disfigure Seiya by cutting off his ear. However, Seiya awakens his Cosmo, the inner energy of a Saint, and turns the tables, severing Cassios's left ear instead and defeating him with the Pegasus Meteor Fist.

This defeat profoundly shapes his character, transforming his arrogance into a deep-seated hatred for Seiya, which is further inflamed when he realizes that Shaina has developed strong feelings for his rival. Despite this hatred, Cassios's most crucial relationship remains with Shaina, for whom he feels devotion and a protective love he believes he can never truly express.

Cassios undergoes significant development during the Sanctuary arc. When Seiya and his friends attempt to penetrate the Twelve Temples to save Athena, a brainwashed Gold Saint, Aiolia of Leo, stands in their way. Learning that Shaina, though still recovering from injuries, intends to rush to Seiya's aid, Cassios is torn. His love for her ultimately overcomes his hatred for Seiya. Knowing that Aiolia's mind control can only be broken by witnessing the death of someone close, Cassios knocks Shaina unconscious to prevent her from going and races to the Leo Temple himself. There, he sacrifices his own life, allowing Aiolia to kill him. His final act is not one of revenge but of selfless love, hoping that his death will save Seiya and, in turn, spare Shaina from the grief of losing the man she loves.

Regarding his notable abilities, Cassios is not a true Saint as he never fully awakened his Cosmo. His power relies almost entirely on his natural, superhuman physical strength, which is far greater than that of a normal man and allowed him to easily defeat nine other tournament contenders. He possesses no secret techniques or the ability to manipulate atoms like a true Saint. However, in his final moments, his intense love and determination allowed him to briefly manifest a faint aura of energy, temporarily boosting his physical resilience against the overwhelming power of a Gold Saint.