PRINCE ZARDOS
Prince Heinell (in Japanese version)
Prince Sirius (in Italian version)

Commander-in-chief of the Boazanian Earth Invasion Forces.Heinell is a hard, high tempered guy, very much like Kenichi. He has no time for romance, and very loyal to Zuzanbazil, the emperor of Boazania. Zardos kidnapped earth people to work as slaves. He had a sad childhood. He never saw his father ...... and her mother died shortly after he was born.  Zardos only knew that his father is a traitor. Because of his father, little Zardos was hated by his peers. That made him want to do the best to clean his name from his father’s stain. Later on, we found out that he is actually the son of Doctor Armstrong (Lagour) from his Boazanian wife Rozalia, so he is Steve's (Kenichi’s) big brother.

Draco
Gael in the Italian version
Jyangyaru Rui in the Japanese version

Second-in-command of Boazanian Earth Invasion Forces.  He is very loyal to Heinell. He used to work with Zuhl and often competed with him in making robots, but after Zuhl was punished to death for treason, he worked alone until later Bergan, a Boazanian Commander, came.  He later killed himself in front of the Voltes team for being a failure to conquer earth.

Zandra
Kazarin Rii(in Japanese Version )
Kazarine (in Italian version)

Robotics Adviser and Personal Adviser to Prince Zardos.  Zandra died in Zardos' arms saying that she loves him. At that time, Heinell realized that he also loves her, but it’s all too late. Katherine saved Heinell’s life several times, i.e: by telling him about Zuhl’s and Zaki’s plan to kill him, by taking Heinell out of his destroyed castle to Boazan, and lastly by giving her own life to stop a an attempt on Zardos' life.

Zuhl

Military Adviser and Minister of Boazanian Ministry of Defense.  He is a snivelling hunchback who will easily connive with either of the warring factions, depending on who has the upper hand.  He was later executed by Prince Zardos for treason.