In the time since the loss of their human collaborators, the alien culture has taken a cold, cruel turn--continuing their work in remote bases in mountaintop facilities, on the sea floor or even on the moon. They search for unfamiliar technology or biological samples from unfamiliar worldlines and disassemble or vivisect it.
Thuu Marth society is divided into three castes: Guardians are the leaders and protectors of the Thuu Marth, overseeing scientific projects and directing efforts to exterminate threats; Abductors run the experiments, finding test subjects and artifacts for study and performing the proceedures; Infiltrators rely on stealth and camoflage technology to live in hiding among the inhabitants of Gamma Terra, acting as spies and assassins for the Guardians. Since the fall of Area 52 in years of warfare with the rival nations of Xi and the Ishtaran Empire, most of what remains are devastated ruins and abandoned Omega Technology.
Real World UFO LoreEdit
Where the information presented on the Thuu Marth in the Gamma World game products is limited, there is quite a lot of real world lore that can be taken as valid since the gray aliens are based on the same lore. According to UFOlogists, the gray aliens come from a world known as Serpo in the Zeta Reticula system. They were originally a slave race of genderless, drones engineered and commanded by a giant race of shapeshifting saurian creatures that used them as a labor force and food supply, draining their psychic energies. They were known as the Olnians (or the House of Oln). It is said the grays eventually rebelled against their masters, but without a natural method of procreation were forced to rely on clone assembly to create more of their kind--they were dying.
It is in this state of desperation that The Gray Emmisary came to Earth, his hope to convince humans to let the Thuu Marth study humans, experiment on them, borrow from them the genetic code required to become a biologically viable race and have natural children of their own. The Thuu Marth went from being entirely Dow, the genderless three-foot-tall rubbery gray drones, to including some gendered members. Known as the Essassani, these Thuu Marth were nearly human height, with visible differences between males and females as well as coloration ranging from a more pale flesh color to an almost orange-gold skin tone. Some of them even began to grow some hair and develop more human-like facial features such as small noses.
From there, what were the Thuu Marth's intentions with us? Turn us into a slave race as was dione to them? Return back to their own world and leave us alone? Use Area 52 as a base from which to launch an interstellar war against the House of Oln? Whatever their intentions the Big Mistake changed all of that and the century and a half of war that followed obliterated their holdings. Now the Thuu Marth exist as scattered enclaves. With the emmergence of gendered Essassaani it's likely some of them grew up entirely outside of their culture amid the multitude of other survivors in the wasteland.