NPC taxonomy

Incidentally, I think this makes
quite a good holy symbol.

Back in the 80s, psychologists came up with what they call the Big Five Personality Traits model for describing people. Their feelings, motivations, methods, etc. I'm not sure it's a good enough model for describing a real-world person with all their complexities, but it seems fine for NPCs.

In this model people are described by where they fall on five sliding scales:

Openness to experience

A character high on the openness scale is going to be curious. A low score will make them cautious.

Conscientiousness

A high score means being prepared, a low score means being spontaneous.

Extraversion

A high score means being outgoing and sociable. A low score means solitary and self-sufficient.

Agreeableness

A highly agreeable character will go with the flow and co-operate easily. Low agreeability means being strong-willed and independent.

Neuroticism

A high score means always on the lookout for trouble, a low score means being confident. 

I don't think that low scores are necessarily a negative thing. I've tried to present them here as being advantages in their own way. The diagram below makes no such attempt:

You, in a nutshell

I use a 10-point scale for convenience. I'm always looking for new ways to categorise NPCs for solo play. Tools to give me an idea of how they're likely to react under pressure, which way they'll jump. I think this one hits the sweet spot in terms of usefulness vs complexity. It also has two other things going for it: 

It has a neat acronym, which makes it memorable. Openness, Conscientiousness, Extroversion, Agreeableness, Neuroticism: OCEAN. As noted before, I like to do my solo play tools-free. Anything that helps in memorising is a plus for that. (It would be better if the terms weren't  multisyllabic words, but that's not how psychologists work.)

It's also broadly compatible with Traveller's planetary qualities model, with a single, simple tweak of stretching the scale to 16 digits. That means that some day a Traveller character may speak the words "Yeah?! Well I colonised YER MUM last night!" and be (mechanically speaking) correct.

Most NPCs aren't going to fall at the extremes of the scale, so for each category I make a 3M10 roll. I roll 3d10, then remove the highest and lowest scores, leaving only the middle one. Charting these rolls would give you a nice smooth curve like the one below.

For the full array that's 15 dice a'rollin', so you could also just click here:

0 0 0 0 0

For my first test I got a result of 7 3 7 4 10. This NPC is curious, spontaneous, sociable, likes to have their own way and is confident to the point of narcissism. I think it's this guy:

I would have liked to see the episode where they 'let him at it'
and he gets punted into a canning machine

That 10 score is an extreme result, occurring in just over 2% of people. There has to be an interesting story in his background to explain how he turned out that way.