No one's ever seen us
The kingdom where we secretly reign
(And no one's ever heard of our band)
The land where we invisibly rule...
As the Mesopotamians!
Sargon, Hammurabi, Ashurbanipal and Gilgamesh!
I like Gutium. What? No, you've probably never heard of it. You probably like Sumer or the Medes. You know, mainstream anthropology. Me, I'll be over here with my can of PBR and the sole surviving information about the Gutian people. See, they never got big. It's all about location, and the Zagros mountains were about as hostile an environment to a people like that as London was to grunge at the height of Britpop. The Gutians were kicking around those mountains - which are in what's now Iran and Iraq - from 2154BCE to about 2050. Basically, the Akkadian Empire - the prototypical Sumerian city-state - collapsed in on itself under the weight of Gutian raids in 2154, and the Gutians were the local bunch of barbarians who took advantage and wandered around ruling southern Mesopotamia until a different bunch of Sumerians kicked them back out again. A half-decent analogy here might be the Visigoths. They didn't quite sack Rome, but they brought their own little dark age to the region, which is one reason we know so little about them. They did manage to destroy the city of Akkad itself, which is one reason why no-one's yet found the site of it, but they were either unable or unwilling to wipe out the local city-states entirely. As such, the city of Lagash had itself a small renaissance unmolested, and evidence of that has survived. There's no evidence the Gutians had much in the way of civilisation or agriculture, and there aren't really any contemporary sources to draw on that have survived. All that later sources say about them seems to give the conclusion that Gutian rulers were singularly inept, letting the land lie fallow, farm animals wandering the countryside, and so on, and so forth.
What's interesting to me is that the Gutians may be being unfairly maligned on this count. There's a fair amount of evidence that by the end of the Akkadian Empire, southern Mesopotamia was in the midst of a fairly dramatic shift in climate - it's known that nomads were moving closer to water sources, and there are abandoned city sites, signs of lower rainfall and river depths, and malnourished skeletons of cattle. Similar things were going on in Egypt at the time, and it's entirely possible that this played a large part in disintegrating the Akkadian Empire, leaving the Gutians with nothing to inherit but a wasteland.
In terms of ethnology, the Gutians were probably Indo-European - Aryan, in the original sense, if you prefer to think of it that way. It's a fairly well-accepted theory that they may have been ancestors to the Kurds; the area that became known as Gutium, between the Zagros mountains and the Tigris, pretty well comprises what's now thought of as Kurdistan. Less compellingly, 'Gutium' sort of sounds like 'Kurdistan' if you have a bad head cold. More esoterically, by the same token it's been theorised that they were in some way related to the Goths, because 'Guti' kind of sounds similar and there's a dubious speculation that they might have been fair-haired. In any case, it's known they spoke a distinct language, but almost none of it has survived. They had a (comparatively) brief dynasty, and a later list of the names of their kings remains the only surviving example of the Gutian language.
So. For posterity, the last surviving words of a people that lived four thousand years ago. Amaze your friends by reciting them. Get a set of bongos and make them into experimental beat poetry. Knock yourself out. The Gutian kings:
Imta, Inkishu, Nikillagah, Shulme, Elulumesh, Inimabakesh, Igeshaush, Iarlagab, Ibate, Iarlagash, Kurum, ???, ???, Irarum, Ibranum, Hablum, Puzur-Sin, Iarlaganda, ???.