Professor Kozo Sakonji, alternatively known as Dr. Hook in select adaptations, operates as a scientist for the Earth Defense Force. Originally mentored by Professor Hamaguchi, he trained to assume command at Camp Big Falcon. When Hamaguchi perishes during a Boazanian assault, Sakonji ascends to lead scientist and commander. His early leadership contrasts sharply with his predecessor’s, marked by stringent discipline and high-pressure training for the Voltes V team. He enforces rigorous drills that occasionally compromise pilot safety, such as mandating perilously high-speed flight maneuvers. After confiscating the team’s personal belongings to eliminate distractions, his methods trigger a temporary rebellion where the pilots desert the camp.

During a subsequent beast fighter attack, with the team incapacitated and defying orders, Sakonji displays tactical acumen by directing them to victory. He declares he would never compel them into unduly hazardous actions, stressing his dedication to their safety. This event becomes a pivotal moment, establishing mutual respect. The Voltes team gradually accepts his strategic counsel, while Sakonji demonstrates increased consideration for their welfare. Their coordination and combat efficacy strengthen under his command, consistently driven by his core objective: defending Earth and its inhabitants.

In the live-action adaptation "Voltes V: Legacy," the character—renamed Larry Hook—maintains this arc with amplified severity. He arrives at Camp Big Falcon immediately following Dr. Smith’s (Hamaguchi’s counterpart) burial and a Boazanian strike that debilitates the base. His introduction features swift diagnosis and resolution of critical technical failures aboard the Volt Frigate, including defusing a bomb planted by an enemy infiltrator. This portrayal heightens his strictness and seriousness, nearly provoking the Voltes team’s resignation. Despite these intensified traits, his role as the successor commander who initially clashes with yet ultimately earns the team’s respect endures. Future fan-fiction plans involve the character within the "All Worlds Alliance" and "XP4" universes. Certain international dubs, including Cuban and Brazilian releases, excised the character entirely due to the anime’s re-editing into a condensed film format.