The Founders were a group of Changelings from the Gamma Quadrant. Though generally considered mythical, they were the ruling force behind the Dominion. (DS9: "The Jem'Hadar", "The Search, Part I", "The Search, Part II")
At one time the Founders were a peaceful, curious race that explored the galaxy, possibly including L-S VI. (DS9: "The Alternate") Unfortunately, their overtures of peaceful cooperation were met with violent rejection and persecution. As an adverse reaction to being hunted and rejected, they accepted the pejorative Changeling as their own and retreated to a rogue planet. They then determined that, in order to be safe, they must set themselves the task of creating order from the chaos they saw around them.
What you control can't hurt you. - Founder (DS9: "The Search, Part II")
The solids have always been a threat to us; that's the only justification we need. - Founder (DS9: "The Search, Part II") Chaos was dangerous as it would allow the persecution to arise once more. Therefore they must have order but this was an order that they controlled, for their benefit and only incidentally for the benefit of the "solids."
Once they consolidated their control they sent out a number of their kind across the galaxy to learn more about any other solids. The two most notable of these lookouts were later known as Odo and Laas. The mission of the lookouts was to learn as much as possible about the solids in their area, and report back. (DS9: "The Search, Part II", "Chimera")
As the leaders of the Dominion, the Founders lead a vast Empire, with the assistance of two genetically-engineered species, the Vorta, to whom they delegate the day-to-day work, and the Jem'Hadar, to whom they delegate most military matters. Both species consider the Founders to be gods. (DS9: "Hippocratic Oath", "Tears of the Prophets")