The Rikti are a race of extra-dimensional beings that have plagued several universes in the now-defunct City of Heroes MMO.
According to information collected by the United Nations global security force Vanguard, the Rikti developed along similar lines to Earth. But then they were visited by what was described as an "alien power" around 2000BC*. This "alien power" exposed them not only to advance technology, but also mutated them into the creatures that they are today. Although they resemble human children at birth, advanced genetics mutate them during puberty into the more repugnant-looking beings as adults.
The "alien power" also invested heavily into a hive-mind thinking for the populace, rejecting any notion of individuality. Rikti think of themselves as part of the greater whole, be it as a group, a regimen, or a species in general. The Rikti also long-abandoned notions of religion or mysticism, which unknowingly created a specific vulnerability to magic.
Contrary to Vanguard propaganda, the Rikti were considered a peaceful race, almost utopian in nature. They learned much from the advanced technology they were given, modified it, and even developed telepathic communication and instantaneous teleportation.
But then a schism broke out in this "perfect world". Ancient records showed that the "alien power" was actually the original "True Rikti", from a world that died out and could not support them. They came to that universe's Earth initially with the idea of working with the humans. But they were opposed by the gods of their universe, who considered the "True Rikti" a threat to their own existence. Unable to reproduce because of what happened on their dead home, the "True Rikti" changed their plans and they began transforming the populace into the Rikti we know today. This is the real reason why religion and spirituality and mysticism were weeded out, because the "True Rikti" did not want their "children" to ever embrace or empower spiritual beings that would threaten their own communal existence.
This revelation shocked the communal species, but it still was not enough to divide the Rikti. The "True Rikti" believed that the truth would eventually come out, but that their "children" would have evolved enough to accept this new information without disrupting the "perfect species" they developed.
Then, at some recent point in their 4000-year collective history, something happened. An extra-dimensional attack devastated the Rikti. The attackers resembled representations of their ancient gods as well as beings known as "humans". This caused the schism to divide the Rikti along political lines as to how to handle this "threat". The side that clearly won out was the one that wanted to wage war across the whole multiverse.
Using the advanced technology they possessed and modified, the Rikti became a whole world obsessed with waging war. They developed dimensional portals to peer into other universes with the intent on finding the home world of those attackers and destroy them utterly.
What they found, though, disgusted them.
Contrary to their own biases, the Rikti were considered the "freaks" of the multiverse, not the commonality that they believed. There were multiple variations of "humans" and "superhumans" and even gods and demigods that were similar to the ones that had attacked them.
The decision was then made to obliterate them all. All the "humans", all the "superhumans", all the gods and demigods, everywhere, in every dimension that they found.
The Rikti war machine went through every world they deemed "the enemy", attacking relentlessly, destroying the defenders of those worlds, and then subjugating the populace, transforming the humans into Rikti. This would ensure that the Rikti would become the commonality in the multiverse.
In most instances, they were successful. They were particularly successful in the universe designated as Omega Xi 6-4, where magic was outlawed. Their brutality left the world completely dead and sterile except for one strong-willed survivor.
There was only one universe that they did not attack, and that was the Praetorian Universe. According to some sources in the Rikti community, the leaders declared that world to be "already dead" thanks to their advanced Hamidon infestation. (The Praetorians would later claim that they successfully fought off the Rikti.)
Eventually the Rikti discovered what they believed was the home world of their attackers, what we deem as "Primal Earth".
The Rikti invaded this world on May 23rd 2002*. The brutality of the attack was global, but it specifically targeted Paragon City, where the Rikti knew "the enemy" was at its strongest. They hit the headquarters of the Freedom Phalanx, devastating it and the neighboring areas. They divided the city itself, putting up huge walls to further isolate the populace and prevent any defenders from stopping them. When the Midnight Squad began fighting back, the Rikti dropped a powerful neutron bomb that obliterated the area and destroyed all of Baumton.
But the heroes of this world fought back, and they fought back hard. They discovered late in the subjugation that the Rikti were particularly vulnerable to magic. It wasn't enough to stop the Rikti completely, but it was an edge they could use to cut the invaders off from their home universe, where an endless supply of troops, vehicles, and weapons were coming through.
In November of 2002, the superpowered beings, heroes and villains alike, joined forces for one final and risky gambit. While the combined forces launched one massive attack at the main occupation headquarters, a smaller team of humans, superhumans, and mystics would sneak across to the Rikti Home World and plant a mystical barrier that would forever shut off any access to the Primal Universe.
The gambit worked. Access to the Ritki Home World and the collective mind was shut down. The Rikti still remaining on the Primal Earth either fought to the death or they went into hiding, hoping that at some point they would be reconnected to their collective mind.
Their isolation was limited to five years. In 2007, the Rikti were able to create a smaller portal to the Primal Universe, which once again allowed them to attack the planet. But this time they were not able to mount a massive invasion as before. The humans and superhumans of this world took the littered remains of Rikti technology and adapted it to their own purposes. They were prepared for the Rikti.
The so-called "Rikti World Invasion" (as the media dubbed it) did cause some damage to buildings, but the threat was minimized by the heroes, so it ended up being a failure for the Rikti and for their dreams of revenge.
(See their Paragon Wiki entry for more information.)
The Rikti were seen in several comics based in the City of Heroes MMO.