Steve Armstrong, eldest son of Boazanian exile Ned (Hrothgar) and Earthling Mary Ann Armstrong, grew up alongside brothers Big Bert and Little Jon unaware of his father's alien origins. His childhood adventurousness shifted to deep responsibility after Ned's disappearance and solidified when Mary Ann sacrificed herself protecting the Voltes team from Boazanian attack.

Leading the Voltes team, Steve pilots the Volt Cruiser, forming Voltes V's head. He possesses exceptional combat skills in marksmanship, swordsmanship, and hand-to-hand fighting, coupled with strategic insight that spots enemy weaknesses. His engineering talent is evident in modifying the prototype Voltman into the functional Black Voltman.

Steve staunchly rejects lethal force against living beings, especially when driven by revenge, believing it undermines the team's moral standing. This principle sometimes causes friction with teammates who nonetheless respect it. He develops romantic feelings for teammate Jamie Robinson, but his hesitation to confess creates tension, particularly with his ex-girlfriend Eva Sanchez. His eventual confession is rejected as Jamie is with teammate Mark Gordon, straining Steve's relationship with Mark and leading to fights.

The discovery that Prince Zardoz (disguised as "Manuel Nobaz"), leader of the Boazanian invasion, infiltrated Camp Big Falcon and befriended the Armstrong brothers to spy, profoundly impacts Steve. He harbors intense hatred for Zardoz after the betrayal is exposed. Their conflict culminates in a duel where Steve wounds Zardoz using a dagger originally gifted to Ned by Zardoz's mother, Rozalia.

Learning of Ned's true heritage creates internal conflict regarding Steve's own Boazanian roots. Following Ned's death, this heritage positions Steve as a potential heir to the Boazanian throne. His leadership style occasionally clashes with authority figures like Dr. Hook, leading Steve to temporarily resign after a mission involving Hook's stricter methods.