Kagemaru is the main antagonist from the first season of Yu-Gi-Oh! GX and he is the leader of the Shadow Riders.
Kagemaru was once the superintendent of Duel Academy. When he left Duel Academy, he became ill and old. In a terrible health, he now hopes to regain his health and youth by sucking the energy out of duel monster cards. He wants to use the three sacred beasts for his plan. Only problem is that they were locked underneath Duel Academy, and protected by seven spirit keys, which he once gave to chancellor Sheppard. He sends the seven Shadow Riders to win the spirit keys. When they all failed, he went to Duel Academy himself. He placed his body in a large machine, which would infuse him with the power of the duel monster cards from all over the world, once he had summoned the three sacred beasts. While dueling Jaden, his youth did indeed return, but once he was beaten, he regained is old age. He then promises to leave his evil ways behind him. His Shadow Charm was a ring. He plays a "Sacred Beast" Deck, which revolves around summoning the three Sacred Beasts.