Dominians

The Dominion was a major galactic political power, whose influence was exerted over thousands of planets in the Gamma Quadrant. The Dominion was founded somewhere between ten to two thousand years ago by the Changelings, a species of shapeshifters who henceforth called themselves the Founders. 
Absolute rule of the Dominion remained in the hands of the Founders and their Great Link, whose decisions could not be disputed under any circumstances. However, the Founders were largely content to leave the administration of the Dominion's daily affairs to the Vorta. The loyalty of the Vorta and the Jem'Hadar is genetically-engineered, which in most cases ensured absolute obedience to the Founders. The Founders themselves were rarely seen, even by their servant races, and were treated as gods or myth. Due to such a social standing within the Dominion, most of what the Dominion's member races carry out are often for the glory of the Founders, or to please them in some way, similar to how religious figures would pray or carry out an action to please their God(s). (DS9: "Hippocratic Oath", "Treachery, Faith and the Great River") 
A Dominion political strategy frequently used is to not use its military might during initial contacts; but take over via influence and espionage. While Jem'Hadar fighters destroyed the USS Odyssey as a show of force, the Dominion used its vast influential and espionage tactics to destabilize the Alpha Quadrant. For example, the Dominion precipitated a war between the Cardassian Union and the Klingon Empire, and then struck an alliance with the Cardassian Union, knowing full well they would accept due to their dire state, so to gain support and a foothold in the Alpha Quadrant before deploying its military power.
The Dominion is comprised of several "member races", as the Founders claim to control the destinies of hundreds of species. The Dominion was founded on the principle of control, with the intent being to neutralize any potential threat to the Founders by whatever means necessary. In cases involving cooperative species such as the Karemma, the extent of Dominion interference is fairly minimal and restricted to material support. However, if the target species is or becomes less cooperative, the Jem'Hadar are dispatched to wipe out any opposition. The fear of massive Jem'Hadar reprisals is enough to keep most planets in line. For a prospective member, at first contact the Dominion may appear helpful, or even benevolent. A typical Dominion strategy is to make concessions in the short term for an advantage in the longer term, which may be centuries in advance.
The more notable member races include: Breen (2375) 
Cardassians (2373-2375) 
Dosi 
Jem'Hadar (military servant race) 
Karemma 
T-Rogorans (conquered 2370) 
Vorta (servant race) 
Yaderans (conquered 2340) 
=== Technology ===
A typical Jem'Hadar attack ship armed with the phased polaron beamBy the time of the Dominion War, Dominion technology appeared to have significantly outpaced that of most Alpha Quadrant species. 
Instead of phased energy or disruptor beams, Jem'Hadar rifles emitted powerful polaron beams which had the side-effect of acting as an anticoagulant in some humanoids, thereby impeding the natural wound-healing process. (DS9: "The Ship") 
Similarly, Dominion and Breen warships displayed more impressive firepower than their Alpha Quadrant counterparts. Phased polaron beams were mounted on all Jem'Hadar attack ships. These initially cut through Federation shielding without effort; ( however, the DS9 crew subsequently managed to adapt their shields to withstand Dominion weapons for short periods. (DS9: "Call to Arms") The Breen also wielded a huge advantage on the battlefield with an energy dissipating weapon capable of disabling Federation and Romulan vessels with a single shot. Countermeasures for these technologies do exist and have proven to be effective. 
Dominion transporters utilized transponders which enabled them to transport individuals across distances as far as three light years.
Dominion warp capability is not very effective compared to most Alpha Quadrant species. A Dominion fighter was capable of at least warp 7 and a battle cruiser was capable of at least warp 4.7.
While Dominion technology was in many cases superior to that of the Federation, the Dominion seemed to possess a deep respect for Federation engineers. One Vorta claimed that they could "turn rocks into replicators". The Dominion relied on the Jem'Hadar for emergency ship repairs when other options were not available.