A groups of aliens known only as the Mysterious Invaders are an alien race who appear with powerful living weapons to destroy humanity and take control of Earth for unknown reasons in a series of verses films and their related media. While they are never given an official name, the Mysterious Invaders are given the name the Damdom and are the arch rivals of the Vegan Empire in Dynamic Heroes. Later iterations would use the Damdom name for simplicity's sake.
In Great vs. Getter a mysterious ship sends an egg onto Earth that later hatches into Gilgilgan. When the beast was cornered by Great Mazinger and Getter Robo in its second form, the ship sacrifices itself to Gilgilgan allowing it to morph into its final form.
The Damdom release their mass produced Pikadron robots upon Tokyo which the Mazinger robots were no match for and had already decimated the Getter Robo. Later they unleashed another beast named Gilgilgan when the Shin Getter Robo was unleashed. The appearance of Mazinkaiser however forces them to change Gilgilgan into a mechanized form and sprout eggs to make more Gilgilgans. Fortunately, both robots managed to destroy Mecha Gilgilgan and Boss Borot destroyed the Damdom ship before it could give the signal to hatch the eggs.
In Robot Girls Z+, the main antagonist Gilgilganko is revealed to be a member of the Damdom and even controls fleets of UFOs.