Frankenzombie is an undead demon serving among the Demon King's henchmen. He stands 6'6" tall with gray skin, facial scars, gray or white eyes, and no visible hair, typically wearing boots. Frankenzombie believes he originated as an ordinary zombie before being pieced together and revived, maintaining his personality remained constant throughout; October 11th commemorates the day he gained consciousness after this reassembly. He exhibits a perpetually happy-go-lucky demeanor, frequently laughing hysterically even during distressing events. Frankenzombie adheres to a live-and-let-live philosophy, accepting Princess Syalis's chaotic actions—including those causing harm or death—without protest or concern. He regularly associates with fellow demons Minotaur, Quilladillo, and Castle Grunt Goblin, forming a recurring social group; Princess Syalis is also noted as an associate. Within this circle, he enjoys reading fighting manga and finds horror movies amusing rather than scary. His sleep talking manifests as constant laughter. Though his real name is Isaac, it is rarely used in daily castle interactions. Frankenzombie functions as a supporting character in both manga and anime, with no documented changes to his core traits or established background.