Kōzō Sakonji served as a scientist for the Earth Defense Force and was a former student of Professor Hamaguchi. Trained to succeed Hamaguchi, Sakonji maintained a professional relationship with Kentaro and Mitsuyo Goh early in his career. After Boazanians captured and killed Hamaguchi using voice imitation technology, command briefly transferred to General Oka at Camp Big Falcon. Oka's struggles managing both military and scientific duties led to Sakonji's permanent appointment as Hamaguchi's successor.

Sakonji swiftly implemented operational changes at Big Falcon to optimize combat readiness against Boazania. His leadership diverged sharply from Hamaguchi's, prioritizing rigorous training and discipline. He pushed the Voltes team beyond prior physical limits, ordering Hiyoshi to pilot at unsafe speeds, and removed personal belongings deemed distracting. These actions sparked immediate friction, culminating in open rebellion when Kenichi discovered his discarded sharpshooting medal. The team abandoned their posts, defying Sakonji's orders to demand Oka's reinstatement.

A pivotal shift occurred when the team, separated during a Beast Fighter attack, faced imminent defeat. Sakonji intervened with critical tactical guidance to extricate them, assuring them he would never mandate excessively perilous actions and emphasizing his commitment to their safety. This intervention facilitated their victory and marked a turning point. Mutual respect subsequently developed: Sakonji demonstrated greater regard for the team's capabilities, while their combat proficiency improved under his strategic direction. This evolving dynamic solidified his role as their trusted advisor. The Philippine English dub renamed him "Professor Hook".