The CW has revealed the alien threat that will unite the DC heroes in the upcoming multi-show crossover.
The villains are the Dominators described as emotionless and calculating, Dominators are masters of genetic manipulation who seek to enhance their abilities to aid in their conquests. They were created by Jim Shooter in 1967 and were an antagonist for the Legion of Superheroes before getting their own limited series called Invasion! in which they facilitate a massive invasion of the Earth.
The crossover will include Supergirl, The Flash, Legends of Tomorrow and Arrow and at first glance seems like an ideal fit for the Invasion! storyline but plot details have yet to be revealed.