Shiro Kanzaki

Shiro Kanzaki (神崎 士郎, Kanzaki Shirō) is the mysterious antagonist of Kamen Rider Ryuki. Shiro is the creator of both the Mirror Monsters and the Card Decks used by the Riders participating in the Rider Battle. He distributed the decks amongst a wide array of different people and personalities in order to find the Final Rider, who would take on his representative in the Rider Battle, Kamen Rider Odin.

Personality
Shiro's an emotionless man, who's only purpose is to save Yui Kanzaki, his sister. His wish to save his sister clouds his vision when it comes to manipulating other people into becoming Riders, knowing full well that the majority won't survive the impending battle. His mind's so clouded, that he used Time Vent at one point simply to save Yui's painting that was ruined by a vase being knocked over. Towards the end of the Rider Battle, the Riders begin to see Shiro's raw emotion in attempting to save his sister, that had remained hidden for a majority of the battle.

Trivia

 * He's the only character in the series who is able to go to both the real and Mirror World without needing to  transform into a Kamen Rider.