Dominators

The Dominators are a race of extra-terrestrial beings.

History
In 1951, the Dominators landed on Earth, abducting humans to gather information about them. They attacked, killing hundreds of soldiers, before leaving the planet.

Sixty-five years later, 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 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.