Soichiro Kuzuki is the Master of Caster in Fate/stay Night. He is the homeroom teacher of Rin Tohsaka and lives at Ryudo Temple. While not a magus, he voluntarily becomes Caster's Master to help fulfill her wish. Kuzuki is emotionless and austere, and became a school teacher to fill the emptiness he felt. He is moved by Caster and disregards any sense of morality to accomplish her mission, coming into conflict with his students Rin and Shirou Emiya.
In the dub of the 2006 series, Kuzuki was played by Patrick Seitz. For the ufotable adaptations, Lex Lang (who originally played Issei Ryudo in the 2006 dub) voiced Kuzuki.