Skyrim's version of Radiant AI was developed from a drawing Todd Howard made on a napkin

With Oblivion Remastered sucking up everyone's time, there's a whole new generation of people getting to enjoy Cyrodiil's weird NPCs—and for us Oblivion vets, it's a chance to reconnect with some old pals. There was so much to love about Bethesda's gargantuan RPG back in 2006, but the vast array of eccentric characters wandering around the world, doing their own thing, really set it apart from the previous Elder Scrolls.

This was down to Radiant AI, which Bethesda has continued to use in all of its RPGs since. And when it came to figuring out how to evolve the system for Skyrim, it all started with a sketch on a napkin.

"The Radiant AI system was developed from a napkin drawing that Todd [Howard] gave us," says Bruce Nesmith, Skyrim's lead designer. Bethesda understandably doesn't want to give away too much about its secret sauce, but Howard and Bethesda have given Nesmith, who left the company in 2021, approval to talk about Radiant AI and its development. "So it's actually a napkin story. You don't hear many of those in real life, but this is a real one."

Howard started by drawing a hero in the centre of the napkin, "and then he drew various little icons to represent things like houses and monsters and whatnot around it and drew a line to them. And he said, 'The player interacts with these things, but they don't interact back with them. That was Morrowind. For Oblivion, we started having them interact with each other a little bit. But now for Skyrim, we want the world to point back to the player as well as interact with itself. So how can you do that?'"

Nesmith sat down with senior designer Kurt Kuhlmann and tried to figure out how to make this work. It was "very freeing", Nesmith recalls. "We went off on our own, and we came back with proposals. Probably some of the most creative moments I've had in the videogame industry, to be honest. And the idea was to be able to have events and objects in the world that the player interacts with and that the code is watching."

One of the early examples they showed Howard connected NPCs, quests and players together. "So you kill a person, and the game knows that NPC has relationships to other NPCs. That's data that we attach to the player. And this is all in the editor. You can see it all. And so it spins up a quest that picks one of the relatives who comes back and tries to kill you. So it created a quest to do that. And Todd really liked that idea."

But Howard wanted to see how this could be employed in a scenario that didn't involve killing. "It's at the heart of all these games," says Nesmith. "They were developed largely by men for the first 30 years. And our more violent tendencies come out in that." It was time for a change.

So he went back and came up with a list of around 30 different actions that the programming could potentially monitor. "Things like, you pick up an item, you steal an item, you change a location, all these other actions that could be taken. We said, 'OK, here's our list.' And Todd said, 'Now that I like, there's all kinds of good stuff in there'."

This led to "large amounts of data" being attached to objects, which was new for Bethesda. "An NPC actor would know the location it belonged to; the location would know the actors that belonged to it. It would know the objects. And we had an event system where, when something happens, it goes through a list of potential quests that could get spun up, that all have conditions on them. If the conditions are met, a quest is spun up. If no conditions are met, no quest is spun up."

It could create interesting conflicts, as different NPCs each had a reason to try to get their hands on a specific object, and the system would draw the closest NPCs to the object, who the player could then encounter, beginning a quest.

This "felt very unique to us", says Nesmith. "The world sees the player. Think of how many games you play where the world doesn't see the player. You kill that monster over there, and the rest of the world doesn't know. You solve this person's problem over here, and the rest of the world is not paying attention."

Nesmith is talking about more meaningful reactions, not simply someone reacting to you killing a dragon by saying, "Oh, I heard you killed the dragon," though Skyrim does have that, too. Rather, his vision for the system was one that could conjure new quests out of your interactions with the world.

"You feel like you're actually part of something that's living and breathing, and like what you do makes a difference. The world sees you. And I'm not going to sit here and say that Bethesda was the first game company to do that, because I don't know that for a fact, but we were one of the early ones. And we were definitely one of the biggest, that got the most notoriety and attention for it."

Of the list of 30 possible actions that the programming could monitor, "virtually all of them" made it into Skyrim. "Most of them made it in, and we didn't actually add very many [afterwards] either, because Kurt and I both have programming backgrounds, so we had a pretty good sense for what would be good and what would not be good for the programming side of it."

The wackiest version of Radiant AI, the version that's present in Oblivion, is the one that's always going to stick with me the most—it was weird and janky and hit me at a formative time. But that doesn't make Skyrim's version any less impressive. Even now, well over a decade later, it's striking how it manages to craft a seemingly infinite number of bespoke quests and adventures every time you cluelessly wander into a dank cave or saunter through a new village.

So thanks, Todd, for doodling on a napkin.