Geronimo Junior, also known as Cyborg 005, began as a Native American man enduring severe employment discrimination rooted in pervasive racism against his people. Forced into a nomadic existence by his inability to find stable work, he accepted a deceptive job offer from Black Ghost operatives—initially presented as construction work or distant employment. This choice, born of necessity, proved a trap. He was abducted and subjected to extensive cybernetic modifications in a Black Ghost laboratory, emerging as the fifth model in their 00 Cyborg line.

His enhancements amplified his considerable natural strength to immense levels, granting near-indestructible armored skin. As the team's physical powerhouse, he effortlessly lifts and hurls massive objects like boulders. Despite his imposing combat role, he exhibits a gentle, reserved, and deeply spiritual nature. He maintains profound reverence for nature, often meditating and observing the world, with this spiritual connection occasionally manifesting as a non-cybernetic sixth sense. This allows him to detect shifts in nature or others' emotional states, a trait emphasized in the 2001 anime adaptation.

During story arcs like "Conclusion: GOD'S WAR," Cyborg 001 unlocked his latent psychic abilities, further augmenting his strength beyond baseline cybernetics. Typically quiet and introspective, he remains a steadfast team member, embodying a peaceful demeanor that contrasts with his function as the group's muscle. His backstory of racial prejudice and Black Ghost exploitation underscores themes of resilience and preserving humanity despite mechanical alteration.