Ludwig Frankenstein was the son of Henry Frankenstein and the older brother of Wolf Frankenstein. Living in the town of Visaria with his daughter Elsa (no mention is made of Elsa's mother, so it can be assumed Ludwig was a widower), Ludwig Frankenstein was a medical doctor who specialized in brain surgery: specifically, in treating individuals who were diseased of mind with the help of his colleagues Dr. Bohmer and Dr. Kettering, the former being his old mentor. Following the apparent deaths of Ygor and the Frankenstein monster at the hands of Wolf Frankenstein, Wolf gave to Ludwig both his own scientific notes as well as those of their father.
Not wanting the people of Visaria, much less his own daughter Elsa, to know about the unsavory history of his family, Ludwig kept the notebooks locked away, determined not to let the sins of his father and brother haunt him. But little did poor Ludwig know that neither Ygor nor the Frankenstein monster were dead. The ghastly pair turned up in Vaseria, and Ygor demanded that Ludwig use his special talents to heal the monster's sick brain, or else he would spill the doctor's secret to the townspeople of Visaria.
Initially, Ludwig agreed, but after the monster killed Dr. Kettering in an unprovoked fit of violence and tried to abduct Elsa, he angrily changed his mind and planned to disassemble the creature, despite Ygor's threats. However, the spirit of Henry Frankenstein appeared before his son and implored him to reconsider, persuading Ludwig to use his talent at brain surgery to simply give the monster another brain to replace the abnormal, criminal one. Perhaps Ludwig was merely hallucinating, but, in any case, he was properly inspired to do just was his father wished. He made plans to remove the monster's brain and replace it with that of Dr. Kettering, whom both her and Dr. Bohmer viewed as a model citizen. In doing so, Ludwig hoped, he would end the threat of the monster forever and clear the Frankenstein family's name.
Unfortunately, the doctor's dreams were dashed when Ygor persuaded Bohmer (who was secretly jealous of his former student's success) to put his brain into the monster's head and not Kettering's. But when the differant blood-types ensured that Ygor's brain could not survive within the monster's body, the creature went berserk and destroyed Ludwig's laboratory. It is assumed that Ludwig perished in the flames.