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The Designer's Notebook: What Evil Lurks in the Hearts of NPCs?

January 16, 2004

I haven't designed many characters over the years - certainly not action characters. In an action game, the avatar character's appearance is all-important, because he or she will be in front of the player 99% of the time. Whether it's someone tough like Lara Croft, cute like Mario, goofy like Crash Bandicoot - or a mixture of all three, like Ratchet - the visual design of the character dominates other considerations. Toby Gard has written an excellent introduction to the subject in his Gamasutra article "Building Character". Non-player characters (NPCs) tend to get similar, but less detailed, treatment - their visual appearance is tied to their role, and their role is usually either hostile or helpful, with nothing in between.

Steve Meretzky, too, has written an excellent Gamasutra article on character creation. His article, called "Building Character: An Analysis of Character Creation" discusses visual appearance and motivation as well. He offers a useful list of questions to which you should have answers if you want to create a character with a background, a person who seems to have some depth.

There's something of an open question about how detailed an avatar character should be, because the avatar is, after all, a stand-in for the player. Most of the time they only do what the player tells them to, so their decisions are the player's decisions. Avatars have to be at least reasonably likeable, and somebody that you want to keep alive rather than actually kill off yourself (like, say, the guy in Postal). Avatars used to be a complete cipher with no personality at all, but lately they've been getting more detailed, and players don't seem to be complaining. But the place where we really have freedom to explore characterization is in the design of non-player characters. That's where the player will notice it most, and that's what I'll concentrate on in this column.

That guy in Postal.

I want to take Meretzky's discussion a little farther. We often speak of characters in fiction as possessing "dimensions" - "I didn't like that movie, the characters were completely two-dimensional," and so on. What do we actually mean by this? Not spatial dimensions, obviously. Rather, we mean that the characters are lacking in some quality that would make them seem more human. I believe that the quality lacking is variety: intellectual, behavioral, and above all, emotional variety.

I'm going to propose a system for classifying characters according to their "dimensionality." It hinges upon the idea of emotional variety. Rather than try to give a formal definition, I'll use examples from the James Bond universe that I think will illuminate the idea.


A zero-dimensional character is one who exists in fixed emotional states, without any variability. In the Bond world, any of the Big Bad Guy's nameless henchmen is a zero-dimensional character. Ordinarily they're only alive for about five seconds, from the time it takes them to see Bond and shoot at him, to the time it takes him to shoot back and kill them. Their only emotion - if you can even call it an emotion - is a desire to kill Bond. Occasionally, for comedic effect, Bond turns the tables on them in some clever way and causes them all to run away in panic. They have no sliding scale of feelings; they just have a "hate state" and a "fear state."

In a video game these NPCs are usually found as enemies in simple action games like platformers. Not only do the characters have fixed emotional states, but those states are only relevant to the player. They have no affection or enmity towards anyone else; they don't help their buddies or even grieve when they die. In fact, they're usually not aware of them at all. The only thing they know about is the player.


A one-dimensional character has a sliding scale of emotional expression. We use this a lot in games: an affinity relationship characterized by a single variable. With one number, you can define an emotional state that runs from hate to neutrality to love, like this:

Figure 1: The emotional state of a one-dimensional character is easy to understand and predict.

In a Bond movie, this is the Big Bad Guy's love interest. She's innocent but deluded. Somehow the Big Bad Guy has managed to keep his army of ninjas, hidden missile base, and plans for world domination secret from her. (BBGs seem to prefer girlfriends who aren't too bright.) She loves the Big Bad Guy, or at least likes him enough to hang around with him, and she dislikes Bond because he's a cocky show-off. Eventually Bond is able to prove to her what scum the Big Bad Guy is. Her affection for Bond goes up, and her love for the Big Bad Guy slides down to hate. (This make's Bond's eventual triumph sexual as well as mortal - not only does Bond kill the BBG, but takes away his girlfriend too.)

Bond girls are not subtle; certainly not fully human, but they're marginally more interesting than a 0D character. They occasionally show a little anger or pride, and they quite often show fear, but their only meaningful emotion is a sliding scale between love (combined with loyalty) and hate. They have two of scales, one for Bond and one for the BBG, and they usually work in direct inverse proportion. No Bond girl ever regrets the loss of her relationship with the Big Bad Guy - the good times they used to have together, their hopes of starting a family, and so on. That would add an additional dimension that Bond movies don't explore.

This is about the level of the more sophisticated adventure game or RPG characters. Each character has an array of single-valued affinity relationships, one with the player and one each with the other NPCs in the game. The player's actions can cause that value to change, and this is reflected in the character's behavior. Less often, the other NPCs can also act to change their affinity relationships with each other as well. However, most NPCs are not designed with a desire to be liked. They don't make much effort to improve other NPCs' opinions of them.


Now we're beginning to get somewhere. A two-dimensional character is capable of feeling a variety of emotions along a variety of scales, as long as they don't conflict with each other. In the Bond world, this is Bond himself. Bond enjoys a great many things: good food and wine; driving fast cars; taking great risks; promiscuous sex. He dislikes the KGB, drug barons, and megalomaniacs. He has a sense of duty, but not much of honor or patriotism. He feels a vague obligation to rescue his bed partners when they get taken hostage, but that's as far as his commitment goes. He only occasionally loses his temper, mostly when someone tries especially hard to kill him. (It doesn't bother Bond when someone tries to kill him once or twice. It's perseverance that really annoys him.)

The important point about Bond's various emotions is that they are never inconsistent, because they don't interfere with each other. Bond is never of two minds about anything; never uncertain what to do; never faced with a moral dilemma. If he does have a conflict of emotions (having to kill a woman that he has slept with, for example), he has a clear rule for resolving the problem: duty trumps love (or lust), and he never mourns about it afterwards. All that Bond really faces are challenges to be overcome one after another, like - ah-ha! - a player in a video game. They're mostly physical challenges, rather than emotional or intellectual challenges, anyway. Bond's emotional mechanisms are quite adequate to deal with the types of problems that he encounters.

Many years ago I had a job in which I had two bosses. One was honest but thoroughly unpleasant; the other, friendly but a bit of a scam artist. It was a weird situation. But there's nothing that says honesty must accompanied by good manners. We consider them both to be virtuous and so we expect them to go together, but they don't have to. Although these qualities are not emotions, it's a good example of a pair of variables that don't interact with each other.

Figure 2: A two-dimensional character's various personality attributes don't necessarily need to be in synch with each other-a good or bad guy could be quite dishonest, yet sickly sweet and polite at the same time.

In the world of videogames, The Sims is probably the game that most closely approximates 2D characters. The behavior of each Sim is governed by a variety of feelings and needs. Not having seen the code, I don't know exactly what mechanisms are in use, but I can tell by observation that the Sims are capable of feeling affectionate, jealous, angry, bored and so on. If they do experience contradictory emotions, there's a rule that determines which one governs their behavior at the moment. Unfortunately, their animation is not sophisticated enough to reflect a complex internal state. You can't tell the difference between a Sim who's cooking dinner while feeling jealous and one who's cooking dinner while feeling bored. Only the double cone over their heads gives a clue to their mental state, and it merely displays a univariate "happiness" value between red and green. (If Maxis had wanted to, they could have used the entire RGB color space, and displayed three values in the same mechanism; but that would have required the player to remember that blue means sleepy while yellow means alert, or whatever.)


For a three-dimensional character we have to leave the Bond universe entirely--because it doesn't contain any. A fully three-dimensional character has the complex hodgepodge of emotions that we all feel, including some that are directly contradictory. A 3D character can love and hate at the same time. Children abused by their parents often experience this condition, which does bad things to their heads.

Figure 3: A three-dimensional character is much more human like than those discussed earlier, and adds realism to the gameplay.

This is an extreme example, however. Three-dimensionality doesn't mean that people are psychotic; it just means that they have a wide range of emotions and, if the circumstances are right, they can occasionally be faced with conflicting impulses. This happens all the time in real life: a person can be honest but greedy, find a lot of money, and have to deal with the contradictory emotions this creates.

I'm a big fan of the sea-novels written by Patrick O'Brian, two of which were recently made into the Peter Weir film Master and Commander: The Far Side of the World. The books are set in the British Royal Navy of the Napoleonic Wars. They're filled with high adventure, but also a great deal of 19th-century science and culture. Most important, however, is the interaction between the two protagonists. Captain Jack Aubrey is bluff, cheerful, and politically conservative, a brilliant military tactician whose eye for the ladies and financial naïveté tends to land him in hot water ashore. Dr. Stephen Maturin, the ship's surgeon, is irritable, perceptive, an enlightened liberal (he believes in radical ideas like democracy, of all things), a hopeless landlubber, and an opium addict. In spite of all this they are great friends, lovers of good food and good music, and vigorous opponents of Napoleon - Aubrey from his sense of duty as a military man, Maturin out of personal conviction. Over the course of 20 novels, we come to know them very well indeed. Their strengths are sufficient to lift them above the mass of humanity and make them admirable subjects for a series of novels; their weaknesses are sufficient to have a profound impact on their lives, but not so severe as to make them unlikable or pitiful.

Part of the key to the richness of their characters is their variability. Like real humans, they are not always consistent. Though you can predict what they will say on a certain topics (Stephen bitterly opposes slavery; Jack is a firm believer in monarchy) they have good days and bad days, times when they are warm-hearted and generous and others when they are sour and intolerant. Jack, though usually jovial, suffers from occasional bouts of depression, especially after a battle. Stephen's irascibility seems to evaporate when he is around children. Their emotions don't simply change as part of the plot, like a Bond girl's. They also change for other reasons and sometimes for no reason at all, moving tidally like the restless sea with which they live.

Unfortunately, my example demonstrates one of the fundamental limitations of visual media. Words are an excellent way of illustrating internal states of mind; pictures are not. The Master and Commander movie, good as it was, displayed only a fraction of these two men's emotional ranges. A film director simply can't convey in a two-hour movie what an author can in 20 novels, or even in one if it's highly introspective. And ultimately this limitation applies to us in the game industry as well. We won't be able to conduct extended character studies in video games. Fortunately, it's unlikely that we'll need to. Video games are about interactivity, and that is where we should devote most of our attention.

That doesn't mean, however, that all our non-player characters should be the equivalent of Mario's turtles or Sonic's piranhas. There is merit in striving even for what you cannot reach, so long as you continue to get closer to it. I believe we should go on working towards the goal of creating three-dimensional characters in our games, firstly because advancing the state of the art is a worthwhile aim in itself, and secondly because it will enable us to make new games for new markets: people who are tired of cardboard characters.

In Fahrenheit 451, Ray Bradbury imagined what he thought of as a dreadful scenario, a future in which people don't read books, but participate in interactive soap operas through wall-sized television sets. Well, people aren't going to stop reading books, because as I've shown, books can do things that other entertainment media can't. But I would like to make the other part of Ray Bradbury's nightmare come true: the interactive soap operas. And that will require characters that we want to care about--characters that we believe are real.

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