trancejeremy
Adventurer
Lawful good originated as part of the nine point alignment system, which is AD&D, not O- or Basic D&D. (Did any of the supplements introduce it before AD&D?) Back in the late 70s, there were disputes as to whether it was good or bad for the game to adopt the 9-point system.
This may seem a mere quibble, but it does tend to reinforce the suggestion that pinning down the core of D&D isn't utterly trivial.
It actually appeared for the first time in the Feb 1976 issue of The Strategic Review (the forerunner to The Dragon, and later reprinted in the Best of the Dragon vol 1).
Basically he drew a two axis diagram, one with good-evil, the other with law and chaos, and mapped out various creatures and such.
The lawful/good classification is typified by the paladin, the chaotic/good alignment
is typified by elves, lawful/evil is typified by the vampire, and the demon is
the epitome of chaotic/evil. Elementals are neutral
He also pointed out there was not a lot of absolutes but a lot of gradations between the extremes
Personally I think they should have stuck with the L/C/N system, since I agree with Moorcock that the extremes of either Law or Chaos are what leads to evil