The Controllers are a subspecies of the Oan race.
Originally a blue-skinned race of humanoids, after billions of years of evolution the Controllers became pink-skinned and hairless. They remain many powers of their Oan progenitors, immortality, flight, psychic abilities, etc.
After Krona violated the law in peering to see the beginnings of the universe, his act caused a schism within the Oan race. The mainstream Oans believed evil needed to be contained, however the more radicals believed that believed needed evil to be destroyed. These radicals would leave Oan and become the Controllers, a force that would be continuously at odds with their brethren and their servants the Green Lanterns.
The Controllers moved to another dimension, and dedicated themselves to developing weapons would be used to destroy evil. Among their weapons are the Sun-Eaters, gaseous beings that could devour whole planets and stars; the Miracle Machine, a device that can turn any thought into reality.