I've read dozens if not over a hundred articles on ways to generate NPCs. One of my favorite heuristics is the simple list of coming up with the following for each NPC:

1. Things they want to say
2. Things they don't want to say
3. An active secret

However, I was thinking that even this isn't fast enough. It doesn't tell me anything, and if I had to list out a dozen NPCs on the fly like this, maybe quite a few people can, but for those who haven't done a lot of improv, this is going to be hard. Of course, these tools help, but I thought I'd share how I come up with NPCs.

All of these methods involve pulling from memory, but not in a "I AM TRYING TO MEMORIZE THE CHARACTER" kind of way, but an "oh wait, I know this person" kinda way.

Generators

If you're looking for names on google, one of the first things that's gonna pop up is fantasynamegenerators.com. Here's a pic of a random name generator I found here:

Just spam the male/female (and sometimes they have gender neutral) name button, and see what pops up. Honestly, this is likely the least interesting way, and I usually reserve this method for Unnamed Guard no. 1, Unnamed Guard no. 2, and Bartender 503. Generally, they are similar. Maybe they have a few different quirks, but if you need something quick and dirty, use this, and act generic. It's more common IRL than you think - a lot of cashiers have the same vibe (not all of course, but you know what I mean), fast food chains have people in uniforms to be more similar, and etc.

STEAL FROM MEDIA

I recently watched an Interview with the Vampire. Check this handsome vampire...

This is Lestat de Lioncourt (now say it again in your head with a french accent), and if you've watched the show, you know a little about him, if you've read the books, you know a lot, and if this is the first time you see him, you know nothing. Regardless of which of these 3 you are, it's a good thing. Act like how you think this guy would act. All our versions of Lestat will be different, and that's great. Now go back to that fantasy name generator website, and look for the French version. Pick a random name that sounds nice, and boom. INSTANT NPC. If the players like him, you can start to think of what his secrets are, and what he knows that he's wiling to tell the players, but basically instantly, you have an NPC, you know how to act him out, and maybe you're just missing a couple of details about his knowledge. Regardless, this handsome lad is gonna be easy enough to play on the fly, and if you need to add more details, you have some Wikipedia pages to skim through.

Now do this with literally any media. Movies, anime, TV shows, cartoons, comics, books. Bonus points if you listen to audiobooks and find audiobooks that don't have book versions. At least in my circles, surprisingly few people listen to audiobooks, and I can't recommend Impact Winter, ABC Murders, and any other audiobooks that don't have a physical version (at least, for now). You can also look for the books based on the Forgotten Realms if you're looking for more traditional D&D stuff, but I think you can figure out the rest here.

Emphasis, you don't need the deep lore of the characters in their worlds - in the end you're going to have to reshape them to your lore. Their characterization is compelling, how would they act in your setting?

Scryfall

Scryfall is a website used by magic the gathering players to search for cards. I, the D&D game master, use this to come up with characters. go to scryfall.com and click on advanced search and you should see something that looks like this:

In type line, just type in "Legendary" and "Creature". You'll get a list of thousands of cool creatures with lore that you can google. Sure, the first seven creatures are gonna be Aang from the Last Avatar (they just had a magic set come out), but after that it's a long list of inspirations! You can also do this for locations, if you type in "Land" instead of "Creature" or for item ideas if you type in "Artifact".

If you're looking for a specific type of creature, you can type it in, and you'll most probably find something. As with the article on prepping for a new campaign, I needed a lot of faeries, and I couldn't find much lore online (besides reading more Irish mythology books). I typed in "Faerie" and it gave me 20 cards. 20 is more than enough to come up with a family of noble fae, and along the way, I'm pretty sure I'll be inspired to create at least 2 or 3 more of my own.

Now that I've introduced Name Generators, Stealing From Media, and Scryfall, the final method has arrived...

Not Unique Enough? Mash Them Together

I went on a craze recently when I explicitly logic-ed this. I had always done this, but it was always subconsciously. I had just recently finished My Hero Academia and found that Shigaraki was a pretty compelling villain. Then I started thinking - who are the other most compelling villains I've seen before, as my own opinion (reference method 2 above). I came up with the following list:

1. Tomura Shigaraki from My Hero Academia
2. Sephiroth from Final Fantasy 7
3. Sosuke Aizen from Bleach
4. Renoir from Expedition 33
5. Conquest from Invincible
6. Dio Brando from Jojo's Bizarre Adventure
7. Darth Vader from Star Wars
8. Krampus from... Christmas?

I simply mashed them together, one pair at a time. Shigaraki and Sephiroth were combined to create Kairon Vex (randomly generated Kairon, added Vex cause Vs and Xs are cool letters), a villain with a tragic backstory; combining Sephiroth's fallen angel aesthetic with Shigaraki's instant destruction and childish tantrum driven behaviours. A hero-turned-destroyer (like Sephiroth) with the ability to can decay anything he touches. Take the best (or worst) parts of their personalities and track it. EASY.

Let's do one more, let's do the last two, Vader and Krampus. Lord Vader... Lord Krampus... I wanna keep the "lord" part. Lord Vadgrim, the Punisher. A fallen Paladin (Vader aesthetic) who is methodical in nature to punish the wicked (Krampus), while carrying a sack of souls (also Krampus). Imagine Vader's dark armor with a winter motif. Maybe Horns that stick out of his helmet. Maybe a tiefling of some kind? I could keep typing by just stealing my favorite parts of these two characters.

Now you can do this with any type of character. Pick your two favorite side characters, and smash them together. Samwise Gamgee with Alfred Pennyworth. Loyal to a fault, reasonable, and have different skills. Pick which would be most useful for your game. You can do this for ANY GENRE. Mix Spock from Star Trek with Agent K from Men in Black. DO IT. Then tell me what you've come up with. I'll reply with some of the other NPCs I've made, so we keep this organic expansion going. 

Tata for now, and don't forget, who's awesome? You're awesome.