Hogback, also known as Doctor Hogback, is a world-renowned surgeon whose reputation within the medical community was nothing short of legendary before his disappearance. A native of the West Blue, he was celebrated for performing miraculous operations that saved countless lives, an achievement that earned him every possible award and title available to a physician. He was considered a genius on par with the most extraordinary of medical practitioners. At some point, he became affiliated with Gecko Moria's Thriller Bark Pirates, serving as a key member of the crew's elite officers, the Mysterious Four, where his skills were instrumental in creating Moria's undead army.

Despite his genius, Hogback possesses a personality that is the inverse of his abilities. He is immensely arrogant and narcissistic, deeply intoxicated by his own reputation. His view of medicine is purely transactional; he performed surgeries solely for wealth and fame, and he viewed his endless line of patients not as people in need, but as an annoyance and a source of trouble. He holds contempt for other doctors who cannot perform at his level, dismissing them as fools. Most critically, Hogback has absolutely no respect for the sanctity of life, whether living or dead. He sees the corpses he reanimates as nothing more than disposable objects meant to obey him, and he cares nothing for the fate of the living people whose stolen shadows give his creations the illusion of life.

Hogback's primary motivation, which led to his fall from grace, is his obsessive and shallow infatuation with the famous actress Victoria Cindry. Cindry was once his patient, and he became a devoted fan. After amassing his fortune and status, he proposed to her, but she rejected him because she already had a fiancé. Shortly after, Cindry died in an accident. Devastated by her rejection and death, Hogback abandoned his career. It was at this point that Gecko Moria recruited him, offering to use his Shadow-Shadow Fruit powers to resurrect Cindry's corpse in exchange for Hogback's surgical expertise. Hogback agreed, stealing Cindry's body so Moria could reanimate it. In a perverse twist, he did not care about reviving the woman who had rejected him; he only wanted her physical beauty, which allowed him to create an obedient servant who would never refuse him again. Beyond this obsession, he also appears to hold genuine loyalty to Moria, helping him pursue his goal of becoming Pirate King.

Within the story of the Thriller Bark arc, Hogback serves as a major antagonist. He first encounters members of the Straw Hat crew when they arrive at his mansion on Thriller Bark, pretending to be a benevolent researcher studying the dead for the sake of mankind. His true nature is exposed when Tony Tony Chopper, a young doctor who had deeply admired him from afar, discovers Hogback's horrific experiments and his cruel treatment of the reanimated Cindry. Hogback directly confronts Chopper and Nico Robin, unleashing specially requested zombie bodyguards like the swordsman Jigoro (a zombie infused with Zoro's shadow) to fight for him. The battle culminates in a philosophical clash about the ethics of medicine and the definition of life, ending only when the enormous zombie Oars inadvertently crushes Hogback underfoot during a rampage. Despite this, he survives the encounter. Following Moria's defeat at the hands of the Straw Hats, Hogback revives the unconscious Absalom and helps rescue the badly injured Moria, fleeing from Thriller Bark to safety.

Hogback's most significant and telling relationship is with Victoria Cindry's zombie. He treats her brutally, kicking her and forcing her to perform humiliating acts to prove his control, yet he has unnerving tantrums when her pre-programmed personality compels her to serve food without plates or make snide comments about his love life. He is also directly responsible for the physical augmentations of his ally Absalom, using surgery to grant him immense animalistic strength. The relationship with Chopper forms a key part of his character development, as Chopper initially reveres him as the ideal doctor but ends the arc seeing him as a monster more rotten than his own zombies, representing the complete corruption of everything a healer should be. While Hogback himself does not develop significantly as a person, his actions serve as a dark mirror for Chopper's own dream and ethics.

In terms of abilities, Hogback is notably one of the few high-ranking members of a pirate crew who possesses neither a Devil Fruit nor any significant combat ability. He relies entirely on the zombies under his command for protection, though he does display a degree of strategic planning in selecting his bodyguards. His true power lies in his unparalleled medical and surgical expertise. His skills are so profound that he can perform complex modifications on living beings, stitch together disparate animal and human corpses to create functional zombies, and even install a cockpit inside the legendary giant Oars for Moria to pilot. He was able to preserve the hundreds of bodies on Thriller Bark without decay for years, and his work was so highly valued that even Moria, a Warlord of the Sea, sought him out as an essential partner for building his unstoppable zombie army.