The story chronicled the battle between the crew of the semi-transformable carrier Daikū Maryū (also called the Kargosaur in the US version, and also known as The Great Space Dragon) and the Super Robot Gaiking invented by Dr. Daimonji (Prof. Hightech in the English-language version of the show) against an invading race of aliens called the Dark Horror Army from the planet Zela whose home planet is facing destruction by a black hole as their population starts to mutate (the fact that their giant bearded ruler now wears his mouth on his forehead is considered only a minor mutation). Notable aspects of the series include the dinosaur-based designs of the Daikū Maryū and its support machines and the use of part of the carrier to form the main robot. The robot Gaiking was piloted by former baseball star named Sanshiro Tsuwabuki (Sanshiro's name was changed to Aries Astronopolis for the English version with the carrier being called the "Great Space Dragon", a literal translation of "Daikū Maryū". Likewise, for the Latin America version the main character was called Brando Drummond and the carrier "Gran Dragon del Espacio") who was drafted for the job because his latent psychic powers made him the only one capable of doing so, all other similarly empowered candidates having been assassinated by alien agents with he himself having been injured in an attack that ended his sports career. Gaiking is most easily distinguished from other mecha by its skull-shaped golden torso formed from the head of the Daikū Maryū and its golden horns.

The leader of the alien villains was named Prince Darius, and all of their ships and mecha were fish-shaped, which most likely inspired the Darius series of video games.