The warder, while not distinguished with a name, plays a rather important if brief role in the short story "The Last Wish". He is a particularly brutal prison guard in Rinde who decides to beat Geralt senseless as his two colleagues hold the witcher. He is described as taking particular pleasure in this.
Geralt, simply hoping to goad the guard, tells the warder that he wishes the man would simply burst. The plan being that this would enrage the man sufficiently that he would punch the witcher in the head rendering the latter unconscious and limiting the beating. Instead, Geralt's wish is fulfilled, much to everyone's astonishment and the man is reduced to red pulp in a flash.