Galerians are Dorothy's creations that give the title to the series.
They are genetically enhanced humans, the result of the experiments at Michelangelo Memorial Hospital, created with the main purpose to wipe out humanity and serve Dorothy as their god. They all possess psychic and paranormal powers. Similar to Rabbits but different from their prototypes, they have the ability to speak and have free will despite being slaves to their creator in some ways. It's revealed in Galerians: Ash that they are resistant to radiation poisoning due to Dorothy expecting nuclear retaliation in her war with humanity. If they abuse their powers or drugs, they will short, becoming very dangerous but slowly lose their health until death or by stopping the process with Delmetor. Galerians cannot be killed in any of them boss fights by Rion when he shorts, and Rion himself is not killed by Rita's short in the OVA movie.
There are nine confirmed Galerians in the series. The confirmed Dorothy's children can be divided in two groups: the First Galerians, created directly by Dorothy to serve her Family Program and the Last Galerians, created after Dorothy's death with the purpose to resurrect her. The Last Galerians prove to be able to exist also in a world of data like Rion is able to do. It is unknown if the First Galerians exist in the data world the same way the Last Galerians exist because they are only fought in the real world.
Despite being known as the Last Galerian, Ash is also a powerful AI program very similar to Dorothy. He apparently had no physical body and his true form existed in the data world.
The word "Galerian" possibly came from the French word "galérien" which means galley slave, a forced laborer (usually a criminal or prisoner of war) that rowed in a galley ship. There is also the German word "galerien" which is the plural version of "galerie" which means gallery.