Ryuunosuke Uryuu is a sadistic serial killer and one of the main antagonistic figures in Fate/Zero. He is a young, unhinged man who takes pleasure in murder and chaos, making him a dangerous and unpredictable presence throughout the series. He becomes the Master of the Caster Servant and plays a major role in the Grail War’s darker, more horrific events. His character serves to highlight the story’s themes of madness, depravity, and the corruption hidden beneath the Holy Grail War.