One of the great strengths of early iterations of D&D like B/X is their brief treatment of monsters. There are none of the long treatises on each creature's ecology, biology, and society (which really exploded in AD&D 2E, if I recall.) Each entry in the monsters chapter of the rules tells you the monster's stats, what it looks like, what it can do, and where it can be found. That's it. The beauty of this is that it leaves all the world-specific details of creatures to the DM, instead of codifying an "official" version.
Even though these things were lacking in the actual rule books, I absorbed a great deal of what monsters were "supposed" to be like from adventure modules, most especially The Keep on the Borderlands. Gygax portrayed the humanoids as essentially evil, ugly, savage humans. Sure, they looked different, and they hated "real" humans, but they had all the same basic needs and motivations. They ate, drank, slept, reproduced, and reared young. Other modules and supplements that I read and played pretty much followed Gary's lead, and the paradigm of goblins as reskinned barbaric humans became lodged in my mind.
These days, I want something a little more fantastic. I want goblins and kobolds that are radically different from humans and demi-humans, despite their superficial physical resemblance. (I also would like to avoid "orc babies" moral dilemmas, because I really don't find them fun or entertaining.) I'm thinking of something like the dark fey creatures depicted in so many tales. Without further ado, here's the direction I'm leaning...
In addition to humans and demi-humans, the world is populated by fey beings - elemental spirits of nature spawned by the earth itself. Thus, woodlands give rise to treants and dryads, flowers and mushrooms birth pixies and sprites, streams and springs spawn nixies and naiads. But even nature itself is not incorruptible.
There are places where the trees, the waters, even the very hills themselves have grown hateful. They may seem at a glance little different from more wholesome locales, but always they seethe with invisible malice that troubles the hearts of good creatures who venture near. From the detritus of these places - the stinking mud and the mouldering leaves, the rotten hearts of diseased trees and deadly toadstools, the festering darkness within the fouled earth itself - spring the dark fey: Goblins, hobgoblins, kobolds, bugbears, trolls, ogres, and others even more grotesque.
The dark fey, as their less-loathsome kin, are ageless beings, untouched by the ravages of time, although they often are haggard and gnarled in aspect suggestive of ruinous age. Some may take the forms of male or female, but without the functions: they are not born, but generated spontaneously from places of malevolence and corruption, and they know not what it is to be young or old. They need no food to sustain them, but hunger gnaws them nonetheless; eating assuages their hunger for a time but gives them no true pleasure, and what they cannot devour they will spoil so that no mortal may have the enjoyment of it. They likewise do not need sleep. Some partake of it anyway out of sheer sloth, but others despise it and never close their bloodshot eyes. Long years of wakefulness may add the gift of stark madness to their vicious natures.
Dark fey are normally closely bound to the sites of their genesis, and cannot stray more than a few miles without weakening. If forcibly removed, their life force dissipates, and their bodies, bereft of the animating spirit, revert to the stuff of their making: mud, sticks, decaying leaves, slime, mold, and shadows. The corrupted woods and hills which spawn dark fey inevitably produce more to replace any who are slain; they are not quite genius loci, but perhaps more akin to a fungal mass from which sprout an inexhaustible number of mushrooms. Thus the numbers of dark fey tend to remain constant, despite the best efforts of adventurers and mercenaries charged with their extermination. In some cases, it may be possible to purge such a site of its evil influence, but a different method is required for each, and discovering and implementing it is likely to prove an arduous and expensive endeavor. Worse still, sometimes the evil spreads like rot, expanding outward to engulf a larger area. Many a human village has succumbed to the creeping terror of a bugbear-haunted forest on its borders, or a dwarven stronghold overrun by the taint of goblin-earth spreading from a mountain's black heart.
These things the dark fey have in common, yet they are also diverse, with each race distinct from its awful brethren. In our next installment, we will begin the tour through the ranks of these spirits of malice, beginning with the goblin.