DORCONS

Planet of Origin; Dorca, in another galaxy of the Local Group, the same as Psychon.
The Dorcons are a humanoid species looking much like humand who have developed an expansive advances civilisation. They are conquerors who have built a vast interstellar empire. They have been known to have attacked Psychon in the past and use Psychon brain stem to achieve immortality.
Planet Entra and its lunar penal colony Ellna are probably part of the Dorcon empire.
Source: Space: 1999

PSYCHONS

Planet of Origin: Psychon (in another galaxy of the Local Group). Psychon had one moon, similar to Earth's one. As of the end of the second millenium, the planet has become geologically unstable.
Psychons are humanoids looking much like humand who developed an advanced civilisation and some space faring capacities. Some psychons are known to have developed psionic powers allowing them molecular transformation and/or mind control.
After attempted invasions by the Dorcons who abducted numbers of Psychons, the planet was left unstable. Either to find an new home or escape their aggressor, most of the inhabitants of the planet had left it by the beginning of the third millenium, leaving only the scientist Mentor and his daughter on the planet, trying to stabilise it with a biological computer named Psyche. Some escapees made contact with the Croton civilisation. Their insertion was complicated by the attempt by one of them to seize power through mind control.

Source: Space: 1999

THE BRINGERS OF WONDER

Planet of Origin: in another galaxy. By the end of the twentieth century, their homeworld had been sucked dry of all its radioactive material.
The Bringers of Wonders are sentient radiovores that developed some sort of civilisation. Organic masses two meters high by nearly a meter in diameter with one eye (10 centimeters in diameter) at roughly the same height a human would have his, they can be described as: "plasma that forms on some organic matter when it begins to decompose." With very limited mobile capacities and no means of handling physical objects, they communicate through telepathy and use beings of other species under their illusion-based mind control to do their physical work. They seem to be able to survive in the vacuum of space.
After having consumed all the radiations on their homeworld, some of them left in a spaceship with hopes of finding new sources of nurrishment. As spaceship contruction would have been beyond their capacity and it is the only form of hardtech they've been seen using, it is likely that it was stolen from another species visiting their world.
Source: Space:1999, The Bringers of Wonder