From the introduction:
The Greens are reptilian aliens from Alpha Draconis, who want to turn humanity into a slave race as food stock. They stand about seven feet tall, with scaly skin, long necks, snouts, and tails, roughly like a cross between a human and a velociraptor.
The Greens are ruthless killers with no sense of empathy or goodness. They rule a vast empire of 487 worlds and untold numbers of slave races that the Greens use for forced labor, cruel blood sport, and food.
Greens use sophisticated projection technology to appear to humans in any guise they see fit. There are many Greens living among us now as apparently “normal” humans.