The Empire is a military hierarchy with the Emperor of Darkness at the top, the Great General of Darkness at the second highest, the seven generals serving under the Great General, and the Warrior Beasts and foot soldiers at the bottom.
In a flashback, it is revealed that the Mycenae Empire was once a peaceful nation living on the island of Bardos. They mastered the art of robotics, building giant machines called Talos to defend themselves against ther enemies.
In some point of their history, the Empire was taken over by the Emperor of Darkness. Using the Talos units, the Great General of Darkness overthrew prince Kelvinius and enslaved the original inhabitants. At some point an earthquake destroyed the island and forced the inhabitants to move underground, seemingly disappearing from history.
In present times, an expedition to the island led by Juzo Kabuto found the ruins of the Empire's civilization, along with some Talos units. But one of the scientists, Dr. Hell, planning to use them to gain control of the world, used the machines to massacre the scientists so that no one would stand against him. Using their technology, he built his Mechanical Beasts and set his plans for world domination.
In the Great Mazinger series, it is revealed that the Mycenae Empire still survived underground, building their civilization with a series of tunnels that extend around the world, and that Duke Gorgon was a servant of the Great General Of Darkness. It is revealed also that many of the original inhabitants were transformed into Warrior Beasts or enslaved to serve as foot soldiers to run the Mikelos.
Planning to retake the surface, the Great General and the Emperor for a while allowed Dr. Hell to use the Mechanical Beasts on the surface until he was defeated and the Empire began its rise to the surface once he was defeated and getting a general idea of the threat known as Mazinger Z.
While their technology is ancient, it is advanced for its time; the metal used for the Warrior Beasts is made from a unique alloy that is much stronger than steel and human brains are implanted into the giant cyborg bodies.
- As revealed in the files for the original plans for God Mazinger, the Mycenae Empire is revealed to be descended from aliens.