Hiyoshi Gou, also called Little John Armstrong, is the youngest son of scientists Kentaro Gou and Mitsuyo Gou. His father left Earth during his infancy, creating a paternal void partially filled by his protective older brothers, Kenichi and Daijiro; they often treated him playfully despite his remarkable talents.

He demonstrated extraordinary proficiency in automation, mechanics, robotics, and electromagnetism from a very young age. Recognized as a prodigy by multiple university faculty, he mastered complex subjects like quantum mechanics through specialized instruction. This expertise led to inventions such as Tako-chan (Octo-One in English dubs), his octopus-inspired robotic companion.

His multifaceted talents extended beyond academics to aquatic sports, excelling in swimming and diving. These skills proved essential for piloting the Volt Frigate—Voltes V's leg component—specializing in maritime tactics. He joined the Voltes Team as a technical specialist, responsible for critical field repairs and maintenance during operations against the Boazanian invasion.

Throughout the conflict, his journey intertwined with Earth's defense and Boazan's liberation. He contributed to overthrowing Emperor Zambojil’s tyrannical regime, which enforced discrimination against hornless Boazanians. His technical ingenuity and combat piloting proved vital during the rebellion, including the unified assault combining Voltes V and the Solar Bird spacecraft in the final conflict.

His father's absence remained a consistent emotional undercurrent, shaping his reliance on his brothers and dedication to the team. As a child deprived of paternal warmth, this influenced his interactions, sometimes leading crew members to perceive him as naive; he actively sought to prove his maturity. His mixed half-Boazanian heritage also prompted internal conflicts regarding his identity, impacting his relationships with both allies and enemies during the liberation campaign.