Goblins are greedy and crude creatures that live in the mountains. They are slightly shorter than humans and a bit weaker in the muscles, but they are more nimble and there are vastly more goblins in existence than there are humans on Earth.
Goblins have no creation myth of their own, which in itself is slightly mysterious. Their close allies the trolls claim to know how the goblins came into existence, but they are not telling. Scientists of many races have speculated that, as the trolls are (or claim to be) an extremely ancient race they were there to observe it and perhaps have taken the goblins into their confidence.
Suffice to say, at present the beginnings of the goblin species remain a mystery, but their first appearance in "the world of man" is known to all. One day, as a dwarf smashed through into what he believed to be a hollow cave, he encountered the first known tribe of goblins, who are presumed to have lived a totally subterranean life up until their discovery. Goblins began to pour from the hole after learning of this vast new world, and a green tide quickly overtook that section of the dwavern mountains, at least temporarily. How deep and how far their tunnels run not even the dwarves know, nor how they stayed hidden long enough to develop sentience and such a huge underground population.
Your generic goblin is rather like a small child in mindset. It takes what it wants by whatever means it can, and it wants almost everything it sees. On their own, even trained military goblins will flee at the sight of anything even slightly scarier or more dangerous than themselves, but will gleefully attack and torment a lone enemy that looks weak. Goblin emotions seem to get stronger the more of them are grouped together, while a single goblin might not dare attack a single dwarf, twenty of them will happily take on twenty of their bearded foes (and probably lose), however whereas a fleeing lone goblin might quickly stop and turn around to face its fear, a group of them will continue charging away from whatever they are scared of, potentially running for miles. Many new settlements are formed this way.
Goblins operate on a strict caste system (enforced by regular beatings) with brainy goblins (generally tinkers, goblins that make things and wizards) at the top, strong goblins (the military) underneath, useful goblins (chefs and farmers) under them and finally the lowly peons at the very bottom. Oddly enough a goblin's job seems to affect its mindset, not the other way around. This explains the lack of goblins at the very top (who wants to be smart in a sea of happy idiots? Who would want to learn about hygiene in a tower where raw corpses have to be locked away to keep them from being eaten from where they fell?) and the huge amount of goblins in the military. They love to group together in tribes and often, when a tribe gets too big, will kick out any newborns to go and set up their own.
The goblin's racial preferred sports are "smashing things", "war", "nose picking" and "chess boxing" (without the chess and with fifty goblins in a ring with weapons). They love gold, fighting, other goblins, blood (other people's), shiny things, fire, meat (of any kind) and weaponry. They don't like water, blood (their own), other goblins, other goblin tribes, any kind of pain or things that are smarter than them (almost everything). The most common method of goblin warfare is to get a large group of soldiers and then make them charge directly at whatever enemies they can see.
Scientists have hypothesized that the goblins evolves the way they have because of intense overcrowding. Living almost entirely underground, they had two options: Learn to live with one another or become bloodthirsty maniacs.
As goblins are known often to eat their own children and dead (sometimes without waiting for them to actually die), you decide which path they took.
Your common goblin has thick skin like a coat of leather armour and overgrown teeth for slicing through said skin. They can survive having lost 90% of the blood in their body and occasionally regrow lost limbs. They can digest almost anything, but are engineered to live off of any meat they can find on a battlefield (remember that they are mostly fighting each other). They naturally form largish tribes of about thirty to fifty members and develop a pathological hatred of any other tribe. One or more goblins in each tribe undergo a metamorphosis into something known as a goblin mother (although technically no goblin really has a gender). Anywhere a goblin walks he leaves sticky spores, and in underground caverns its almost impossible not to get covered with these, head to toe. Goblin mothers suck them into their comically huge bodies and begin gestating babies at a phenomenal rate. They actually have three wombs and are always producing more goblins to replace the ones inevitably lost in constant inter-tribal warfare.
Before they discovered the world above the soil they probably spent their entire lives in an unending state of warfare and chaos, now they have turned their gaze upon all of the other "funny lookin' things" sitting in the bright sunshine where the goblins have decided they now want to be.
The vast majority of goblins stayed under the ground, but whether the inner workings of these "deep goblins" are any different is yet to be discovered.
Modern Goblin Warfare Edit
As goblins are loath to share their technology with other tribes, each new founding of a goblin settlement will generally start with little more than sticks and work up from there. As a consquence, goblins field a massive variety of technology and troops types, from wooden weaponry to steam powered robots, space ships or magical flying fortresses, and due to each goblin in the tribe's different idea of what weapons are good for fighting, sometimes all of these at once. Due to this it is very hard to make a comprehensive list of what weaponry goblins use, and so I won't. You'll just have to wait and see. Goblins also often enlist the aid of Trolls.