Karl is a tall middle-aged, human mutant man with long black greying hair, a mustache and beard who lives in an Eastern European mountain range located just outside the village, in his inherited coal mine factory that he made into his engineering factory. He wears a long tattered brown coat with a beige shirt underneath, brown trousers, boots, gloves and a wide-brimmed hat, old-fashioned sunglasses, and has a compass, an old fish scale and a dog tag hanging around his neck. He is often seen smoking a cigar. Once transformed, he uses his magnetic powers to transform himself into a huge robot-looking creature with an elongated "neck", two long arms and caterpillar treads that he rides upon and has his mutated face visible. His weapon of choice is a huge custom-made hammer assembled from different mechanisms that he sometimes carries around with him.

Long ago, Karl Heisenberg was kidnapped and subjected to the Cadou parasite experiments by Mother Miranda, who tried to brainwash him into being her servant, with only limited success. Eventually, he, Alcina Dimitrescu, Donna Beneviento, and Salvatore Moreau became Miranda's lieutenants. Among the Lords of the Four Houses, Karl Heisenberg is the only one who held a grudge against Miranda, due to her own selfish desire to revive her late daughter at the expense of the villagers and how she saw their "family" as nothing more than experiments. As such, he secretly planned a rebellion to get his freedom back, building an army of cyborgized reanimated corpses called Soldats, and hoping to use Rose's latent powers to defeat Miranda. At one point, he attempted to persuade Ethan to join him, but the latter refused upon Heisenberg revealing his plan to weaponize Rose. The Heisenberg family was closely associated with the noble Beneviento, Moreau, and Dimitrescu families, and maintained an alliance with them in controlling the region.