Isaac Rosenthal led the Rosenthal Family as its fourth-generation head, perpetuating their centuries-old quest to forge a perfect golem—a godlike being possessing both an immaculate soul and body. This obsession began with the family's founder, Obed, banished as a heretic for pioneering corpse-based golem techniques fused with Kabbalistic artificial souls. Isaac devoted himself to advancing this legacy, merging Obed's methods with Taoist "Hopping Zombie" spells to create Rosenthal-style Necromancy. This hybrid art allowed him to reanimate and command corpses, which he deemed "works of art," expressing contempt when others likened them to mere jiangshi. Operating primarily in China, Isaac harvested countless victims to fuel his experiments. He notably massacred the Li household; when officials investigated, he boasted of his creations before slaughtering them after they scorned his work. He held human life in low regard and dismissed his son Nathan's potential to achieve the family goal, despite Nathan later creating four advanced artificial souls. Isaac ultimately succumbed to disease. On his deathbed, Nathan transferred his soul into the family's artificial soul vessel, Taowu, imprinting Isaac's consciousness to prevent its loss. Taowu lay dormant for generations until the 23rd-generation head, Esther Rosenthal, activated it attempting to resurrect her deceased friend Hirumi. Isaac seized this chance, possessing Hirumi's body and causing physical alterations: slit-pupilled red eyes and cracks marring her face. Through Taowu and Hirumi's form, Isaac contacted a self-proclaimed demon who revealed the path to the Rosenthal ambition: engraving a soul with 10,000 "proofs of death" via a Kabbalistic formula would evolve it to Keter (perfection). While death memories normally dissipate, Academy City's Misaka Network stored 10,031 such records. Isaac manipulated the organization Disciplinary Action (DA) and researcher Hishigata Mikihiko to extract these memories from Misaka 10046. Upon obtaining them, he integrated the formula into Taowu's artificial soul and began constructing a new body to house it. During the construction, Isaac consumed DA members to accelerate the process but was overwhelmed by their collective desire for justice, losing control of Taowu. Esther Rosenthal, previously unaware of Isaac's presence within Taowu, exorcised his soul using Emperor Shun's Blade. In his final moments, Isaac acknowledged failure with the same words spoken at his first death. Isaac's abilities centered on Rosenthal-style Necromancy, commanding reanimated corpses through artificial souls. His techniques evolved from Kabbalistic roots into a unique hybrid system incorporating Taoist elements. After transferring into Taowu, he gained the capacity to possess bodies and exert influence, though this control proved vulnerable to potent collective emotions. His original appearance featured light hair, a turban, and non-Chinese attire. When possessing Hirumi, his influence manifested through her altered eyes and cracked facial markings.