Psychlos are a race of large, furry aliens from the planet Psychlo who serve as the primary villains in the extraordinarily cheesy novel (later made into a catastrophically bad John Travolta movie) Battlefield Earth, by scientology creator L. Ron Hubbard.
Psychlos are humanoids that are much larger and stronger than humans. They are also quite tough, with thick, dense skeletons. They do not appear to be substantially more intelligent than humans.
Psychlos only breathe a peculiar mixture of exotic gases that compose the atmosphere of their home planet. They unimaginatively call this mix "breathe gas". The Psychlo atmosphere contains an unstable compound that explodes in the presence of ionizing radiation. As their tissue is full of this compound, a Psychlo will catch fire if a projectile made of radioactive material penetrates its hide.
Psychlos are prone to an assortment of antisocial behaviors, but these are largely the result of medical interventions (see below).
In the distant past, both the Psychlos and another species developed teleportation technology at around the same time. The two races soon came into conflict as they competed for new territory and resources, and the conflict became a vicious intergalactic war. The Psychlos eventually prevailed, wiping out their rivals. In the aftermath, they took steps to keep any other race from developing teleportation technology that could be used against them. Their scientists developed neurological implants that control Psychlo behavior, making it impossible for them to divulge secrets about Psychlo technology. Side effects of the implants gave the Psychlos an enormous superiority complex and near-psychotic paranoia, causing them to fear and despise anyone who didn't have the appropriate implants and associated behaviors. Consequently, all Psychlos have behavior controlling implants, which are implanted shortly after they are born. Most Psychlos have multiple implants. Female Psychlos have implants which cause them to become comatose if they attempt to learn forbidden knowledge, such as mathematics.
As the only race in the known universe to possess teleportation technology, the Psychlos became the most powerful race in the universe, as they could attack their enemies without warning, bypassing all defenses, and their foes couldn't launch effective counterattacks due to the long travel times required to reach Psychlo assets.
Due to their artificially induced greed and paranoia, Psychlos are hostile toward all other species. They are likely to attack any civilization that they believe presents a threat or possesses assets they can easily seize. They can deploy planet-destroying superweapons via teleportation over intergalactic distances, allowing them to threaten adversaries with genocide if they do not acquiesce to Psychlo demands. Because of their greed, Psychlos are inclined to accept tribute instead of exterminating opponents outright.