Gabiru began as the son of Abiru, chieftain of the lizardmen tribe dwelling in the Jura Forest marshes. His early portrayal showed an overconfident and egotistical warrior, his status as the tribe's sole named individual inflating his sense of superiority and breeding disdain, even toward his father. This arrogance made him susceptible to manipulation by Gelmud, who exploited Gabiru's ambition to spark a rebellion against the lizardmen leadership during the Orc Lord crisis. Believing isolating the tribe from Rimuru Tempest's coalition was vital for survival, Gabiru instead endangered his people. After the rebellion's failure and recognizing his grave error, Gabiru accepted full responsibility. His father, Abiru, exiled him permanently from the tribe, forbidding him from ever identifying as a lizardman again.

Accompanied by loyal followers and his younger sister, Souka, Gabiru sought refuge within Rimuru Tempest's burgeoning nation, the Jura-Tempest Federation. Rimuru's act of re-naming him—overwriting Gelmud's earlier naming—triggered Gabiru's evolution from lizardman into a dragonewt. This metamorphosis altered his physical form, changing his scales from green to purple and granting him draconic wings and larger horns. A subsequent evolution during Rimuru's ascension to Demon Lord further refined his physiology, shifting his scales to a reddish hue and enhancing his horns, also granting him the ability to retract his wings for a more humanoid appearance.

Within Tempest, Gabiru underwent significant personal growth, shedding much of his earlier arrogance. He matured into a disciplined leader, eventually commanding the Hiryuu, Tempest's primary aerial combat force, as one of Rimuru's Twelve Guardian Lords. His responsibilities extended beyond military command; he collaborated closely with the dwarf researcher Vesta in the Federation's research department. Together, they pioneered the mass production of Hipokute-derived healing potions, advancing Tempest's medical and economic capabilities. Gabiru's combat prowess was augmented by the Vortex Spear, a legendary weapon inherited from his father, and unique abilities such as the "Showoff" skill—allowing limited fate manipulation—and his ultimate gift, "King of Moods," enhancing tactical control through barriers and spatial manipulation.

His personality evolved from brash and entitled to knightly and earnest. While retaining energetic and occasionally boastful traits—manifested in dramatic pronouncements like "Ta-da!"—he demonstrated humility, fierce loyalty to allies, and deep care for his subordinates and sister. Souka often monitored his behavior, reflecting their close yet contentious sibling dynamic. Gabiru's comedic tendencies persisted, including forgetfulness mid-battle, such as neglecting to use his wings when thrown airborne. A notable incident in "The Slime Diaries" involved him nearly provoking the demon lord Milim Nava by carelessly declaring himself a "hero" without grasping the title's political weight.

His character extends beyond the main series. "The Slime Diaries" prominently features his eccentricities and earnest mishaps in slice-of-life scenarios. The mobile game "ISEKAI Memories" depicted him in an alternate "zombie gunman" role during the "Mushroom Hazard" event, showcasing a temporary undead transformation while retaining his draconic traits. Trivia notes suggest his name may derive from "Gavial," a crocodilian species.