Gregory, also known as Wolf Bone, is a character from the anime Majin Bone who serves as a troubled antagonist and later a reluctant ally. He is always seen alongside his younger brother, Victor, and together they are known as the Tiger and Wolf Brothers. Gregory is an adult male with brown eyes and shoulder-length brown hair, often styled with a goatee and earrings, and he typically wears a distinctive red scarf or turban. His appearance is completed by a pair of narrow, three-white eyes that give him a sharp and cunning look.

His personality stands in stark contrast to that of his quiet and cool-headed brother. Gregory is characterized as a nihilistic and cynical man who tends to view every situation with ironic amusement, often wearing a smirk no matter the circumstances. He is described as a flashy and unpredictable man who enjoys stirring up trouble. This demeanor, however, masks a deep-seated despair and a pragmatic, self-serving worldview. Having witnessed the horrors of war and the worst aspects of humanity after losing his homeland, Gregory became disillusioned with Earth and decided to cooperate with the alien force known as Nepos Angelis.

The background of Gregory and his brother is one of profound betrayal and loss. They hail from a destroyed hometown where they were betrayed by their own people. After being rescued from a near-death experience by a man named Director Higashio, they were taken to an archaeological site. There, the Wolf Bone resonated with Gregory, and alongside his brother's Tiger Bone, they awakened as Bone Fighters. When the villainous entity Dark Scorpion arrived, Gregory willingly chose to leave with them to gain power, feeling that Earth had nothing left to offer him. For a time, Gregory served Nepos while also maintaining a secret deal with Director Higashio, providing information on the aliens in exchange for the life debt Higashio claimed they owed him.

Throughout the middle portion of the story, Gregory acts primarily as a mercenary. He abandons his agreement with Higashio once he feels his debts are repaid, declaring his intention to side with whomever seems likely to win. When the alien faction Revolt gains the upper hand, he quickly switches allegiances again, becoming a persistent threat to the Earth's Bone Fighters. However, his loyalty to Revolt proves just as fragile. After witnessing the leader Revolt betray and eliminate one of his own comrades, Sokius, Gregory is reminded of the very act of treachery that ruined his own past. Disgusted by this, he turns against Revolt, providing crucial aid to the Earth team and successfully participating in the mission to reclaim the stolen Dragon Bone, even at the cost of his own powers.

In combat, Gregory is the wielder of the Wolf Bone, which grants him the attribute of wind. His fighting style relies heavily on tremendous speed, using swift movements to confound his opponents and overwhelm them with powerful unarmed combat techniques. He works in perfect unison with his brother Victor, executing coordinated combination attacks that make them a formidable duo. His signature special move is known as Howl of Shadow. Later, thanks to a strategy devised by Director Higashio, Gregory evolves his powers to achieve the Iron Bone form, which dramatically increases the size of his bone armor's protrusions and further amplifies his strength, making him one of the few fighters capable of challenging a White Bone user.