An advanced, warlike race, The Vrang had conquered and enslaved the population of Krypton. When the Kryptonians overthrew them and expelled them from the planet, the Vrang developed an enmity that extended to hunting down the last survivor of Krypton, Superman.
A Vrang Ship came upon the destroyed remains of Argo City, and from it's records discovered that Supergirl had been sent to Earth, and that there was another survivor there, Superman. They traveled the ion trail of Supergirl's rocket, and found Earth. The Phantom Zone Criminals were aware of this, and escaped to opposed them alongside Superman.
Powers and Abilities
The Vrang exhibited advanced technological abilities, enough to bind Superman and destroy two other super powered Kryptonians outright.