The Unknown Soldiers, or US (pronounced oos) are the result of an as-yet undiscovered project by an unknown species or organisation that wanted their own controllable army, but didn't want to use GMOs, because GMOS were trackable--not to mention illegal. Instead, they sent expeditions out into deep space and tripped on an unexplored planet. They took less than a hundred specimens from one of the native species (it's not known if this species was sentient or not at the time) and brought them back for use as breeding stock. Breed-your-own soldier. Like build-a-bears, but way more ethically questionable. Since they're not a recognised species in the universe and have no identifiable DNA, they are totally unrecognised and completely untraceable. The actual term for the US (on official paperwork) is 'War Bodies.'
All US are marked with a tattooed symbol on the face and tattooed bands on their limbs that allow for fast and easy field identification. Both the bands and the facial tattoo are actually coded symbols, and therefore vary from individual to individual. Some think the bands might indicate rank and the facial tattoo individuals. Others argue the opposite is true. It's possible the colour is also meaningful in some way. Of course, the rest of the universe is also under the impression they are a naturally-occuring species that has issues with the rest of space for some reason, so maybe that's not a reliable theory.
Gobo here is the result of the very first attempted training methods, which produced not soldiers but uncontrollable killers, many of which suffered terrible psychological and emotional damage that rendered them unpredictably dangerous. They were deemed unsuccessful, but were a valuable source of data and were therefore extremely useful. All but one of the first 29 'prototypes' are dead, however; Gobo is the only remainder, and he was more or less just ditched completely.
Left on his own with no self-care skills and no ability to communicate with others, he's more or less a walking, living ordnance. The effective PTSD and other complications of his existence aren't helping.
Trivia:
Art by Itsubun