Dominators

"But what happens when a man like him inherits abilities like yours? We have seen it happen on countless other worlds, which is why we must exterminate your kind before the scourge of your planet becomes the scourge of ours."

- A Dominator about meta-humans

The Dominators are a race of extra-terrestrial beings. They are conquerors intent on maintaining the status quo in the universe by any means, with the unpredictable meta-humans being their prime targets on Earth.

Earth One
In 1951 of Earth One, the Dominators landed on Earth, abducting humans to gather information about them. After President Ike Eisenhower waited for too long without action, the extraterrestrials attacked, killing hundreds of soldiers. Unbeknownst to them, Steel, Heat Wave, and Vixen arrived and subdued a straggler. Suddenly, the National Security Agency appeared and took them into custody (including the Dominator).

As the Legends begin to interrogate the captive Dominator, Agent Smith appears and has the Dominator pinned down onto a lab table while experimenting on them. This results in the National Security Agency forming a truce to keep the equilibrium of Earth balanced.

In October 1988, an anachronistic baby Dominator was found by eight-year old Ray Palmer, who took it in as a pet and nicknaming it "Gumball". The queen of the Dominators then landed on Earth, attacked Sara Lance, and scanned her mind for information on where the baby Dominator was. The queen Dominator then stormed for young Ray's home. The baby Dominator, along with young Ray and Zari Tomaz, was then tranquilized and captured by the government and had it stored in a lab in the woods near Ivy Town to prevent any possible collateral damage. The Atom, Zari, and young Ray later free the baby Dominator and escape the lab. The baby was later returned safely to the mother and left on their ship.

Sixty-five years later after the incident in 1951, however, with the appearance of meta-humans, especially Barry Allen, the Dominators returned to Earth, prefaced with a warning to Earthly authorities that they meant no harm, though in fact planning war. Four ships crash landed, one of them in Central City, spilling forth with Dominators. This faction kidnapped the President and set up a mind control device in an old salt mine, but this device was eventually destroyed by Supergirl, with the help of The Flash. However, they soon abducted Sara Lance, John Diggle, Thea Queen, Ray Palmer and Oliver Queen, placing them into an induced dream world. They eventually escaped, fighting against the Dominators, before escaping in a pod. As they headed down towards Earth, the mothership followed them. At this time, the Dominators were about finished with their superweapon that they intended to use to wipe out all metahumans on Earth. They threatened to drop it unless Barry Allen surrendered himself in 24 hours, which he refused.

They lowered the mothership down on Central City and begin to drop the meta bomb, while a platoon of Dominators fought the heroes on top of the STAR Labs hangar. Barry placed the high-frequency transmitting devices made by Martin on the Dominators, and Felicity detonated them, effectively taking them out.

The bomb began descending, with Sara in the Waverider attempting to use the ship's tractor beam to hold it up. Firestorm arrives and uses his powers to transmute the bomb into water, successfully saving the planet. The mothership then flies off into deep space. The Dominators' status is unknown after that and it is clearly unknown if they will strike again.

Earth Thirty-Eight
Sometime before Kara Danvers was born, the Dominators traveled to Krypton and performed experiments on a number of people, as well as killing a lot more.

Over a year after Kara became Supergirl, one of the Dominators allied themselves with Roulette, who went into the slave trade on Slaver's Moon after Supergirl dismantled her fighting club, wanting to buy all her human prisoners. Later, while helping the prisoners escape, Mon-El almost gets shot by one of the guards, but the Dominator stops the guard and bows to Mon-El. Some time after Kara and Mon-El's escape, Lar Gand and Rhea arrived on Slaver's Moon and one of the Dominators informed them of their son's exploits and told them that they had gone to Earth.

Powers

 * Super strength: The Dominators were strong, shown when a Dominator hit Oliver, sending him flying off the roof of a building.
 * Telepathy: The Dominators are able to communicate telepathically with others, seemingly also being able to use their own language, despite languages such as English not being their native language.
 * Temporal awareness: The Dominators are able to sense any alterations in the timeline, and the time traveler who altered it. It is unclear whether this ability is of biological origin or advanced technology that can detect time alterations.

Trivia

 * The Dominators appear to act based on fear and bigotry.
 * In the DC comics, the Dominators were also the main antagonists in the Invasion! event. However, to attack Earth they first formed an alien alliance first consisting of them, the shape-shifting Durlans, the fanatically fascist Thanagarians, the supply-producing Gil'Dishpan, the ruthless and deadly Daxamites, the strategic weaponsmiths Warlords of Okaara, the hunkering, slovenly Citadelians, the sadistic and scientific Psions, and finally, the Khund, the "most brutal, most innately savage race of war-mongers in the universe".
 * Also, their defeat at the hands of the heroes of Earth came before the dropping of the meta-bomb, which the Dominators had no knowledge of. Though the Dominators had agreed to surrender, and they left, one of the Dominators, eager to prove his low caste level (the small size of the red mark on his forehead) didn't mean he wasn't intelligent, acted alone and invented and released the meta-bomb, which successfully neutralized all of Earth's metahumans. The non-metahuman heroes managed to travel through outer space to obtain an antidote and spread it with help from the extraterrestrial superhero team known as the Omega Men.
 * The Dominators see meta-humans as a threat to their kind.
 * The Dominators think Barry Allen is a threat due to his creation of Flashpoint. However, it is unknown how they know about Flashpoint.