Karl is a tall middle-aged man with long black greying hair, a mustache and beard. He wears a long tattered brown coat with a beige shirt underneath, brown trousers, boots, gloves and a wide-brimmed hat, as well as a compass, an old fish scale and a dog tag around his neck. His weapon of choice is a huge custom-made hammer assembled from different mechanisms that he sometimes carries around with him. He also wears old-fashioned sunglasses, and is often seen smoking a cigar. Once transformed, he assumes many forms thanks to his magnetic powers and an abundance of metal on the battle arena, but mainly stays as a huge robot-looking creature with an elongated "neck", two long arms and caterpillar treads that he rides upon. His deformed face is also visible.

Lord Karl Heisenberg is a human mutant who lived in an Eastern European mountain range. A genius in engineering, he is presumably the patriarch of the Heisenberg family. He runs the inherited Heisenberg Factory, located just outside the village, and serves Mother Miranda, along with the other three major houses in the mountain range.

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 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.