How broadly are we defining "RPG" here?
If you mean something with a storyline running through it that you're expected to follow, then Daggerfall is probably the closest thing I can think of, as already mentioned.
If you're looking more for an open sandbox, I once observed that Mount & Blade: Warband was the best role-playing experience I'd had in a computer game, but it's all very combat-focused. You've got six nations and, I don't know, probably 150 or so noble lords among them. The lords all pursue their personal activities (mostly patrolling their lands during peacetime, or fighting during wars, with bandit-hunting, attending feasts, etc. mixed in) and the nations will go to war with each other. All of this happens independently of your character, who starts out as a small-time mercenary captain, then can recruit troops, build up a company, fight in tournaments, take on tasks, court and marry, become a vassal, and eventually start your own seventh nation if you so desire. Relations are tracked between the PC, all nations, and each individual lord, including lord-nation, lord-lord, etc., so there's interpersonal interaction with NPCs, albeit very shallow interaction. And it's all simulated in real-time with no pre-planned fixed events or anything of that sort.
The Mount & Blade guys are currently working on a new game called Bannerlords, which should be out Real Soon Now(tm), which I have high hopes for, but I'll be watching here for any other suggestions you might get, too.