I don't follow studios...so, I'm just going to list some of the NPCs that had the most influence or which I have the most persistent fond memories of.

The Gold Box games, Pool of Radiance, Curse of the Azure Bonds, Secret of the Silver Blades, Pool of Darkness...played all of those...played a Gateway and Treasures of the Savage Frontier and Champions of Krynn too. The gameplay has really not aged well, though Gold Box Companion adds a lot of QoL upgrades that make it good.

Vampire:The Masquerade - Bloodlines, very cool game.

City of Heroes - From Third Wave Beta to shutdown, great superhero MMO, easy to play as an entirely solo experience, generally only played with family and other friends or just completely solo. (yes, there's private servers out there, I am playing on some of them.)

The Secret World/Secret World Legends = Let's punch Cthulhu in the face! Yeah! Get to be a nigh-immortal superhero...sort of like being in a grimmer version of City of Heroes with worse travel options...but still cool stories and again, very solo-able (to a point)

Neverwinter Nights and Neverwinter Nights 2 - I've replayed the original campaigns of these so many times. I prefer NWN2 because it has more character build options, but they're both great.

Sword Coast Legends - I know a lot of people dislike this as a D&D game and it isn't a D&D game even if it is a Faerun game. I enjoyed the story and the characters...and some of the bosses were quite clever. I wish it had done better so we could have seen more expansions on it.

Lord of the Rings Online - Such a weird mix of nerding out and nerd rage....amazing game for any Tolkien-fan...even when you're complaining about the small odd things they got wrong.

Vampire: The Masquerade - Redemption - Also a very cool game: Pissed off Cristoff.

Pillars of Eternity - I love the reputation systems and it's a wonderfully pleasant dark fantasy storyline.

Shadowrun Returns / Shadowrun: Dragonfall / Shadowrun: Hong Kong - All the three of the recent Shadowrun games are good, but Shadowrun: Hong Kong just is amazing. So good. Though I have to give real props to whoever wrote/designed the companion characters in Dragonfall....oh man, Glory struck a nerve in a wonderfully emotion stirring way.

Grim Dawn / Titan Quest - Like with LotRO, Titan Quest is great for a mythology nerd....though it is a LOT more "got it wrong" than in LotRO. Grim Dawn is basically the same system of Titan Quest with some severe upgrades and an entire extra layer to the characters builds that makes for some wonderful replayability.