Little is known about the nature of one of, if not the, galaxy's first civilized space-faring people. What Federation archeologists have gathered from automated recordings left behind on the few crumbling outposts that have been discovered is that they were highly advanced for such an early period in the universe's history. As the Preservers ventured out into the still young galaxy in search of intelligent life they soon learned the fact that they were alone. In a divine effort of procreation they seeded the galaxy's oceans with genetic material in order to influence the development of life on those planets to evolve into a form similar to their own. Thus began the trend of humanoid life throughout the Milky Way.
It has also been speculated that they had contact with an early form of the Borg. Possibly their creators as well. It has also been theorized that their was a terrible war between them that ravaged countless worlds. In an effort destroy the Borg they constructed the Doomsday Machine. Just as they had the power to create, they now would now have the power to destroy.
The Preservers vanished long before most of their progeny crawled out of the ocean.
Though they disappeared their story doesn't end with them. The meddlesome Metrons ,along with the passive Organians, are long thought to be the descendants of the Preservers and had long ago elected to carry out their predecessors' work. They have played a hand in the relocation of an untold number of species including humans.