Orcs are perhaps the quintessential low-level D&D monster, and one that has been adopted by a range of other RPGs and computer games since. Unlike my earlier ponderings on D&D fantasy creatures, I'm not here going to focus much on what orcs might be like biologically; they're pretty clearly anthropoid beings that, some minor features aside, are broadly similar to humans. Instead, I'm going to look at some different conceptions of them down the years, focussing mainly on D&D itself.
Orcs, in the modern sense, are, of course, the invention of J.R.R. Tolkien. He borrowed the word from Old English, in which it's usually translated as "monster", and is possibly just a less common alternative word for "ogre". But it was Tolkien who introduced the concept of the orc as an evil race of humanoid beings, from which Gygax obviously took his inspiration when writing D&D. Tolkien's orcs are the result of twisted experiments on elves, and are typically described as sallow-skinned and misshapen, although there does seem to be some variation among them. They exist primarily as the foot-soldiers of more powerful evil entities.
1E
Orcs appear in D&D right from the beginning, in which they are an evil, tribal, race of often subterranean humanoids. In 1E (that is, the 1977 "Advanced" edition), they are one of five evil tribal humanoid races, which form a distinct game mechanical hierarchy of increasing physical prowess. Orcs are the third step on this chain, the mid-point against which one could argue that everything else is measured. With no special powers, beyond the ability to see in the dark (which almost everything has) and exactly one hit die, they're pretty much equivalent to starting humans and are about as "default" a monster as one could wish to find.
