It is unclear exactly how long the Psychlos have been in existence, but records extend back several hundred thousand years.

The Psychlos are physically large—about nine feet tall, weighing somewhere near a ton—and have the strength to kill a man with just one blow, making them a force to be reckoned with.

In order to survive in Earth's atmosphere, Psychlos have to wear special breathe-masks over their faces. They also have other physical attributes that tend to make them look a bit strange and ugly, such as different colored fur, sharp talons in place of fingers and an extra talon on their right paw.

For fear of revolt, the Psychlos refrain from creating colonies, and planet Psychlo, or "home planet" as it is called, runs all of the Psychlo operations, including those of Intergalactic Mining and other large companies.

About three hundred thousand years ago, the Psychlo economy was highly dependent upon ore and metals, with mining as its primary business. At the time, however, the Psychlos were in an economic mess, with mobs and unemployment and heavy depressions. Added to this was the fact that they bred like herrings and had a massive population to deal with.

About two thousand years later they encountered a race known as the Selachee, who have banking as their main industry. With the Psychlos' exclusive control of teleportation and shipping arrangements it was very easy for the Selachees to help them build markets for their metals. The Psychlos became prosperous and developed more ways to mine, and the Selachees saw to it that they were economically stable.

Then suddenly, from the Psychlo point of view, an awful thing happened—another race stole or invented teleportation. It terrified them. It is unclear what happened next; however, it seems that this other race (Boxnards, Universe 6) tried to put teleportation to military use. The Psychlos got there first and the entire seven planets of the Boxnards, and every single Boxnard and races associated or allied with the Boxnards, were wiped out. It took the Psychlos years to execute it, but no one ever found any trace of the Boxnards after that.

After about half a century of reclusion following this event, the Psychlos reemerged as the cruelest, most sadistic oppressors any universe had ever seen. However, they were in deep internal trouble again and went to the Gredides System and actually begged the Selachees for help. They wanted money to hire soldiers and buy arms. Of course, the Selachee government (and every other race in sixteen universes) wanted nothing to do with them and it looked like outright war.

They were then turned over to Lord Loonger (a Selachee) of the Galactic Bank and a deal was made—the Galactic Bank would handle all economic concerns and peace conferences for the Psychlos in exchange for teleportation services and protection. It was because of this deal that the Psychlos were able to stabilize and become the strongest force across the universes.