Karl was one of the assistants of Dr. Septimus Pretorius. Along with Ludwig, he helped Pretorius rob graves to get the parts needed to create the bride of Frankenstein. When a fresh heart was needed for the bride, Pretorius had Karl go out and murder a young woman and take her heart. When the bride was being brought to life, the thunderstorm agitated the Frankenstein monster, and Karl tried to cow the creature with a lit torch. This had the opposite effect, as the monster threw Karl from the laboratory roof and killed him.