There was once a great race of humanoids, long before any of our planets had life on them. They were the only ones of their kind in the galaxy. They thrived for ages and spread through our entire galaxy, and beyond. They started using genetic engineering, in order to speed up their evolution and enhance their genome, pushing their biological potential to the extreme.
The procedure had many risks. Though it gradually changed and improved the very fabric of life, and made them immune to all illnesses, they soon realized that it also made them sterile and that they would be unable to reproduce and would die out in a generation. Even if they would use cloning to preserve themselves they would suffer from increasing errors in their DNA.
They decided to seed most of the planets in our region of the universe with the original humanoid DNA, which would be incorporated into the early life forms that just started to develop, and guide their evolution to eventually produce humanoid life forms very similar to the original humanoids. This way there would be a permanent monument to the existence of the humanoid species. They also coded a message into many genetic fragments and spread them across the galaxy, to tell the new humanoid races from different planets of their origins, and to bring them closer to each other, and it was hoped that they would have to work together in friendship and companionship in order to piece together the program that activated the message. This finding was already discovered in the Alpha quadrant, although it was made possible to them only by the coincidental existence of a warp highway which allowed the humans to reach distant spots of our galaxy and collect DNA samples from there. It was essentially just blind luck that they discovered the message, and the profound explanation of why intelligent life in our galaxy is so similar in shape on almost all planets. The spokesman in the ancient message was the leader of the group of original humanoids who seeded the galaxy with their genes.
But even after they seeded the galaxy, they still were not willing to just let themselves die. They decided to keep enhancing themselves using their technology, since it also given them longer life spans and greatly improved their biology. They decided to trust their invention and to continue with the transformation they were going through with their extreme genetic manipulations. Their organic structure continued to improve and evolve, until they were no longer humanoids. They became beautiful higher beings. But they also discovered that their unnatural rapid evolution had a negative side effect; an evil monstrosity was accumulating and growing in them. To free themselves from this destructive influence, they tried a procedure in which they extracted all that was dark and evil from themselves. But the excretion they shaded off had a mind of its own and turned into a creature in itself. A creature whose powers were nearly as great as its evil. They abandoned the dark creature on a deserted and isolated planet and moved on and away.
Free from the negative elements, they evolved even further, becoming more beautiful and biologically advanced then ever. Their organic structure became so complex that it was no longer limited to our lower plain of existence. They had transformed into higher beings, with shape shifting powers. They could not only rearrange their subatomic structure by will, but also to shift their mass in and out of the space-time continuum.
The "Founders" are actually the ancestor race of all humanoids. The Changelings traveled throughout the galaxy, looking for a new purpose. Different groups of them separated and went to different places, each small group that left the main group degraded, and became a race of less advanced changelings, who quickly forgotten their origins. But the main group of changelings, which continued to evolve because they were bond together as one entity in a great link, which also stored all of their joint memories over the billions of years, ended up in the Gamma Quadrant. They discovered that when they join together in a great link and combined their powers they can create new changelings identical to themselves. They found an isolated place where they could study themselves and live out their newly found existence. Since time passed differently for them while they were in the link, they didn't notice how fast the billions of years had passed. It was now nearly 4 billion years since the time they seeded the galaxy with their old humanoid DNA, and they decided it was time to explore the galaxy and learn how much it has changed. They knew that their 'offspring descendents' should be fully developed by now, and wanted to make peaceful contact with them. But the new humanoids feared their advanced ancestors, and hunted them down and killed many.
The Changelings, shocked and terrified from their bitter experiences, retreated back to their isolated world, and from there started founding the Dominion, almost 10,000 years ago. They knew that the only way they could truly be safe was to control all the other races. They did not wish to punish those who hurt them, only to seize control over them in order to guide them to an enlightened way, so that they would stop harming themselves and others. They wanted to bring all their descendents back together, under their rule as their parents. They started mixing races they conquered, either by choice or by force, creating better ones, and using them for their glorious armies that would bring peace and unity to the entire universe. 2,000 years ago, the Dominion was already the strongest power in the gamma quadrant, and by now it is the only major power, the rest of the quadrant either became part of the Dominion or was brought down to cinders.
The top priority of the founders is to protect themselves, because they are the superior race and must survive no matter the cost. Since it proves difficult to conquer the Alpha Quadrant by the easy way, it will have to be necessary to destroy some of the major opponents that face us, especially the Federation. But do not worry, we will keep genetic samples from them for study, to see what good properties could be taken from them that developed during their unique evolution.
Their goal is to create a hegemony of life in the universe in which there would be no violence or suffering. They want to bring order to the chaos they caused. They will try to unite the different races together under their divine guidance. When their plan is fulfilled there will be no more war or illness. There will be prosperity and health to all. Everything will be united in a glorious new order of peace, friendship and love. The cause justifies all the means it would take to achieve it, including the means of violence that sometimes have to be used to destroy the demons that infect some of the races. The Founders will achieve their goal of an ultimate universal peace no matter what it takes, even if it's necessary to completely destroy all those that can’t take place in the new order.
When the original humanoids underwent the transformation, they no longer had the need for technology to survive. They left their homeworld to travel the galaxy, and took nothing with them. About 10 million years ago a newly developed humanoid race, discovered the original humanoids' homeworld, and took over all their ancient technology. With it they started building a new civilization. They created new technologies, more advanced than our galaxy has ever seen. They built a network of corridors through the higher dimensions in which they could instantly reach any point in the galaxy they wanted.
The Iconians. They are also called the Ancients. Like the Founders eons later, the Iconians were also met with fear and aggression from the newly formed humanoids in our galaxy, and decided to take control over them in order to protect themselves and to change the evil ways of the young humanoids. Of course part of the reason for forming their empire was also their selfish desire for material treasures, unlike our noble Founders who only seek to bring order and prosperity to all. The Iconians craved more and more material things and nothing was ever enough. A small group of Iconians decided to leave their society, and set off to find a new home that would be isolated from the threats of other worlds. They formed an individual community, self-contained, peaceful, with the incredible technical sophistication of the Iconian culture, which provided for every citizen’s daily needs, allowing them to devote themselves to culture and art rather than for territorial conquest as the rest of the Iconians. They called their new community Aldea. They evolved a very primitive way of living: for whatever is taken, something is given in return.
It's given them peace. Unfortunately, there are very few of them left to enjoy it. Most of them died out because of sterility caused by radiation poisoning. Their ozone layer started to deteriorate when they started using their cloaking technology a thousand years ago, when many more races developed interstellar drive, to hide their entire planet and go unseen by marauders and other hostile passerby who might rob and plunder. After the hundreds of centuries that they were living in isolation with no material needs, they forgotten how their technology worked.
The Iconian technology continued to progress, they were building more and more advanced Gateways, and were on their way to become the new rulers of the universe. The Iconians wanted to upgrade their physiology, and started using artificial genetic enhancement, gaining special abilities such as healing powers, but then something happened; some sort of deadly plague infected them. The plague effected not only the Iconians themselves but also every other people that came in contact with them, with everyone else dying from it a lot faster than the Iconians themselves whose advanced biology made them live longer with the disease and not die from it right away.
Knowing that the Iconians were spreading the plague while not being effected themselves, and believing that they were infecting the galaxy deliberately in order to totally conquer it, the other developed races decided to wipe out the threat.
Despite their overwhelming technological superiority, a massive interstellar rebellion formed against the Iconians about 200,000 years ago, forcing their survivors to leave their homeworld through one of their gates. It is believed that they all died out at a distant location, but a few of them ascended and became higher beings that now reside in some higher dimension. It is possible that the creatures who live in the wormhole are in fact the Iconians, who evolved into an existence beyond linear time and forgotten about their origins. In any case, unlike the Founders, they left our plain of existence and left us all to rot. They became demons, not gods. The Founders however, chose to sacrifice their own heavenly destinies and stayed in order to help the young life forms that were left bickering among themselves in our chaotic universe. They did not want to abandon us to be consumed in hellish flames, they want to create a paradise out of our universe. And they are still working toward this end till this day.
The radical changes in the fabric of life which created all humanoids is a far cry from the gradual changes of natural evolution. The fact is, without the Founder's genetic guidance, life would still be at its infancy on our worlds. Or worse still, we might have all evolved into monsters. The Founders used the planets that could support life as sanctuaries that would enable the glorious humanoid civilization to endure. That was part of their great plan.
A lot of humanoid races on different planets died. It worked almost exactly the way it was supposed to. You might call it a bio-social experiment, on a grand scale. The experiment was set up to test the humanoid life. Not only were all the seeded planets different from each other in their physical characteristics, the genetic sequencing seeded on them were also not always identical to each other. Some humanoids were programmed to develop directly from reptiles, others from amphibians, yet others were designed to develop after only 6 billion years. Some had been programmed to have more males than females or vice versa. They each had a unique set of circumstances designed to test the developing humanoid occupants, to see how well they adapt to different environments and with new genetic characteristics that were programmed into them. On most planets, the evolution was programmed to end up leaving only one humanoid species on the same planet. Only on a few planets the evolution was directed to allow the coexistence of more than a single supreme humanoid species. The planet Xindus for example, was programmed to produce half a dozen intelligent species, to see the way their cultures would coexist with each other. The physical conditions were also an important part of the study. Some planets had not enough water or minerals on them. Others had too much radiation. Each planet had different environmental conditions. There were truly countless number of variants to ensure an infinite diversity in the humanoid life forms. It's interesting to see the way that despite the different conditions, in almost all cases life somehow managed to assume the general humanoid shape. This proved how strong biology really is. It was also interesting to study how the psychology of humanoids would turn out to be on the different planets. Although some species moved into the extreme, most planet produced a version of humanoids which was very similar to the original ones.
Earth was a special case. That planet was selected because the conditions there were identical to those of the original humanoids' planet, and the implanted genes were also identical to the original primordial humanoid species, to produce humanoids that would be the most similar to the original ones. Earth was supposed to remain isolated until the subjects were needed. Earth's inhabitants, Humans, were, in scientific parlance, a control group. This way the Founders always had a point of references to the changes they made from their original selves. Earth was supposed to be the only planet in its area of space with intelligent life, to make it more isolated and protected, and Earth solar system itself was chosen specifically to provide natural protection for Earth.
Than that damn plan didn't work as it was supposed to. All humans would have died if not for the heroic efforts of few individual humans who managed to save humanity in each of the last several generations. Besides, humanity spread out into the galaxy quickly, the Earth didn't stay isolated. That doesn't seem to fit in with their plan. An unfortunate, and unforeseen, accident. However, as I turns out, a rather fortuitous one.
Long after the seeding, Earth accidentally happened to be located right in the center of many focal points of warp highways, which made the Earth such an important interstellar planet. The humans spread into space far faster than they were supposed to. But, as it turns out we needed a powerful peace-seeking but war capable race such as humans to bring weakness to the quadrant, otherwise one of the more radical races might have taken over, and we'd have a much harder time conquering the Alpha Quadrant. But thanks to humans and the vast pacifistic federation it had built, the quadrant is now less ready for our take over.