Very little is known of the alien invaders from Mortax and the series did not intend to explain much of them. In the original, "War of the Worlds", the aliens originate from Mars. Since Mars is a dead planet and presumably any presence of an indigenous civilization would be noticed from earth, it made sense to change the origin of the aliens to a faraway solar system.
It was a shame that the series did not capitalize on the episode, "Angel of Death". The unexpected, ironic, and somewhat twisted humorous ending would have made for a much more interesting second season had the original plot line been followed. As it was, some viewers, including myself, disliked the second season's post-apocalyptic setting and stopped watching the series.
I present here my own speculative analysis of the aliens from Mortax, for anyone curious enough to read on.
Most likely the inhabitants of Mortax originated from a tightly controlled, rigid, caste-driven society. The upper caste was smug in its superiority over the lower caste classes, even those presumably of a high class, such as scientists. The ruling caste or upper classes which ruled Mortax probably were probably a hereditary class which may or may not have included a military class as a subsidiary upper caste.
At some point in its history, the lower caste classes of Mortax gained political power enough not to overthrow the current ruling caste but enough to gain comparable political parity and most importantly, respect.
As a result of this paradigm shift in Mortax civilization, the upper ruling class now had to address the lower classes with respect. They now called the lower classes, 'comrades'. The lower classes could now address their heretofore upper caste rulers as, 'advocates', not, sir, ma'am, majesty, excellency, highness, lord, mistress, or any other such title conferring superiority over the claimant and inferiority over the one saying it. But it is very clear from the comments of the often frustrated Advocate triumvirate that the bigotry of the upper castes over the lower castes is still very much alive. But now it is politically incorrect to say so in front of them.
Mortax civilization was now unified and moreover, unified in its new, overriding goal, the salvation of its race, civilization, and culture. Unfortunately, the smug racial superiority and bigotry of the upper caste were now subsumed by all of Mortax society. The new inferior class fit only for extinction were the humans of earth. The invasion of earth is an invasion to humans. For Mortaxians, it is a 'colonisation' of a habitable planet regrettably infested with inferior biological sentients called humans whose existence is expendable. The invasion is a fight to the death for all of humanity.
