Ryuunosuke Uryuu is a villain from the light novel and anime series Fate/Zero. He is a serial killer and the Master of Caster during the Fourth Holy Grail War. Unlike the other Masters, however, he has no interest whatsoever in obtaining the Grail and merely wishes to use Caster as a tool for his killing spree. He is voiced by Akira Ishida in the Japanese version of the anime and Johnny Yong Bosch in the English version, the latter of whom also voices Izaya Orihara and Tohru Adachi.