Dungeons and dragons: First description or explanation of the RPG games in ODnD?

Does anyone know where the first reference / explanation of the role play exists in OD & D (beyond "I am x class")? Dave Arneson is often credited with the advent of what we would consider today as a role (speaking in characters to NPCs), but he left TSR to publish on his own. I have never had a copy of The First Fantasy Campaign to see.

Heck, where are the first mentions of NPCs as NPCs and not combat statistics? Something more than Sage's description as a Blackmoor resource.