That's where the Eld come in. Being very ancient, intensely chaotic, and amazingly adept at magic, the Eld are my catch-all explanation for many of the monsters in my campaign setting (the other being the Thulians). In addition, I decided early on to limit myself only to the humanoids that appear in OD&D and to use their descriptions as the basis for my own, with a couple of exceptions. Reading Monsters & Treasure, it's clear that there's a "continuum" of humanoid creatures, beginning with goblin/kobolds and working upwards by Hit Dice. I decided I'd take that idea and find a way to make sense of it. What I came up with was this:
- OD&D implies that goblins and kobolds are the same creatures, the only difference being that kobolds are weaker physically. I'd already decided that goblins are one of the few genuinely aboriginal races of my setting; kobolds will be the degenerate mine-dwelling versions thereof. While I like the scaly dog-men versions of kobolds a great deal, Gary often said that that version was, like so many other D&D monsters, based on a miscommunication between himself and the illustrator, Dave Sutherland. Gary originally envisaged kobolds as evil wizened, gnome-like creatures, as in German folklore. So, I'm going with that, albeit one that complements the "little green men" version of goblins I'm using.
- Goblins are, in their natural state, not very nice from a human perspective: greedy, selfish, and with a penchant for cruelty. But they're not willing servants of Chaos. That's where hobgoblins came in. They were magically created by the Eld as taskmasters and "drill sergeants" to keep ordinary goblins pressed into Eldritch service in line. They're now "independent operators" but still enjoy lording it over goblins when they get the chance.
- Bugbears are another magical mutant of goblins, created by the Eld as shock troops. I can't make up my mind as to whether I'll go with the Monster Manual appearance of these guys or stick with Greg Bell's wacky pumpkin-headed version.
That about covers the basics. I'm still pondering what to do about giants and trolls, but I've already decided that ogres are human beings cursed for having indulged in cannibalism and have now become monstrously ravenous eating machines.