NPCs can clutter notes and references, Aside from the usual hostile monsters , mobs , creatures , etc., to better distinguish NPC types I group my distinctive non-player characters into standard, deities, and background characters . In a couple of my games, I tag some NPCs as location characters .
Background characters (BCs) are generally fluff story elements that are likely never to impact the PCs directly. PC family members, especially distant ones usually fall into this category, legends, rumored, and the countless in crowds. I like to work up a few details about. Any BC can potentially jump over to NPC status.
Location characters (LCs) are places that are also characters. Similar to deities, player characters will rarely directly interact with an LC personality, but LCs often pull on threads of fate, influenced by and meddling in the affairs of their inhabitants.
Deities meddle. They have their own agenda. They share their actual plans with no one. Deities push the big picture and minutiae. Deities are the unknowable movers and shakers that prove nothing. They become NPCs when they start interacting with the PCs. Primal forces can be characters too, but I usually slot them into the deity group. Of course, assuming the PC are not deities.
Named: These NPCs have a name, they have a listed motivation and usually a short paragraph about them. Shopkeepers to the King, gods even.
Unnamed: The “40 orcs” in the key. They might have a group description that applies to all of the above.
Any NPC can step out and be the center of attention. “The game world” does not see the power bars over people’s heads or treat anyone as if they work under different rules.
I started out writing down pertinent notes for NPCs on index cards in a recipe box. I just add anything useful/noteworthy as things go along. Never wasted time on statting them unless it became something relevant to a game or whatever. Just stuff like Big Hands, Bushy Beard, Long Braids, seriously nit-picky, bad gambler, etc. A mix of physical and psychological quirks and whatnot. Listed any grudges, debts, or experiences with PCs as well. Works pretty well.
As for Background NPCs and all that, I tend to note what their specialties and interests are, so I can always find a few reasonably decent potential Hirelings, Patrons, adversaries, rivals, etc. Including potential henchfolk, hirelings, experts, etc. So in that regard, the whole box is mostly just Background NPCs.
Serious, Named, Exceptional NPCs tend to arise through the gaming, often in direct reaction/response to the PCs efforts and doings, so they often get promoted from out of the recipe box to more detailed sheets, which I’m now converting into Scrivener to better keep track and sort them out.
I’ve never considered creating named categories for my NPCs. Some are more relevant than others, but that is usually due to their prominence in either the setting as a whole or their degree of involvement with the PCs. So, I guess “Major” and “Minor” would be my categories? Or maybe “Incidental” and “Reoccurring”?
As for what I record about them, once they last more than a single encounter, thereby upgrading from the “who cares” category to the “Now I need to remember this pretend person” category, I will usually have a name, a brief description of their appearance, any distinctive mannerisms, behaviours, and a note on their voice (yes, I do voices) if it is distinct. Sometimes I will mention a class and level if it matters, the same for a particularly standout stat, ability, item, or knowledge they possess. Here’s a made-up example of what I mean.
Malcolm Grimsby:Old human male, Ranger lvl 2. Lives in Putnam Turn. Hunched posture, creaky voice, tends to natter on about his suspicions of anyone he hasn't known for years already. Wears a big floppy green felt hat and a heavy green wool cloak, both of which have seen better days. He knows where the entrance to the collapsed Barkdale Mine is, but won't tell just anyone as he thinks it's too dangerous for people to be nosing about.
Not every NPC note would include all of the above, sometimes it might be as little as:
Farrow Beckemsham:Owner of the Round Pig Tavern in Putnam Turn, spits a lot and speaks with a lot of 'aow' sounds.
Off the top of the Maltaarano key. Some have more some less.
Baker: (H-10 yellow) There is a sufficient non-householding resident population to support a full time baker here. Most small towns don’t have that population. Maltaarano does.
Everything from basic loaves to sweets. The shop smells wonderful and is always slightly warm. This is a cross between a commercial bakery and a neighborhood one. Most of the bread goes to the school. Plenty still goes out the front door as well.
Harlin Elsoria - Half Elf male - Proof that not everyone in town is a half Centaur. Harlion settled in the village some 20 years ago and decided to fill a meed. Fighter4, ac 12 , pd 20, bab +4, cmb +7. cmd 19
Stats S 16 +3, C 15+2, D 14 +2, I 14 +2, W 13 +1, Ca 14 +2, Psi 4 +9
Saves F+6, R+2, W+2
Knife 1d4+3 +7
HP 33
, mobs 
, creatures 
, etc., to better distinguish NPC types I group my distinctive non-player characters into standard, deities, and background characters 
. In a couple of my games, I tag some NPCs as location characters 
.