Great Mazinger:

The son of Juuzo Kabuto and Kouji and Shiro's father. Was believed to be dead after a lab experiment that apparently killed him and his wife, however, he was saved by Juuzo after being revived as a cyborg.

While in hiding, he improved on his father's robot designs to create the machine Great Mazinger. He raised the orphans Tetsuya Tsurugi and Jun Hono, training them to be pilots.

Shin Mazinger:

The father of Kouji and Shiro and the son of Juuzo Kabuto. He was present at the excavation of Bardos Island and together with his father created the robot Energer Z, the prototype of Mazinger Z. While excavating the Mycenaean technology on Bardos Island, his cyborg body was possessed by the bio-mechanical Kedora and he betrayed the team. He was presumed to have died during the escape from Bardos Island, at the hands of Tsubasa.