If we're talking Fallout; Probably Ian from Fallout 1. ED-E, Arcade and Veronica from Fallout: New Vegas.
If we aren't talking about Fallout. Kuo and Zeke from Infamous 2 were fantastic characters and thoroughly well written, fantastic game.

Thats an easy question. That character would be Zimos from Saints Row The Third. Its not everyday you get to partner up with a guy speaking through an autotune mic.

In Fallout NV, that's a few people, but Private Morales was one I would've liked to have seen added to
after you carry her husband's dead body away from the Fiends' hideout. You get a discount from the
doctor at Camp Mccarran later, but it doesn't seem enough to me. Oh well...

Other games? That's nearly every NPC in FO4, since Bethesda decided to barely give them anything to
do other than short random lines and not many quests. I watched AlChestBreach's playthrough when
the game first came out and saw a child and her grandfather or something talk to each other, and it
made me want to know what they were going to do - which was nothing else, sadly.

But I really liked Malon in Ocarina of Time and her counterparts in Majora's Mask Cremia/Romani. More
from them would've been awesome as well.

Frank Woods from COD Black Ops, never have I seen a character that stole EVERY scene in the game

Ranger Josey from The Better Angels.

https://www.youtube.com/watch?v=y-moiLs5TC4

In fallout my favorite character may have to be adult MacCready from Fallout 4, I did enjoy his annoying kid self in Fallout 3 though. I know a lot of people didn't enjoy his story from Fallout 4 but I myself loved it and I love seeing him go from Mayor MacCready, annoying turd with a helmet 10 sizes too big, to badass merc sniper MacCready. I also love the little things about his character like how he tries to avoid cursing to keep a promise that no one but him would know whether he broke.

Outside of Fallout however, I'm going to be "that guy" and say Solaire from Dark Souls lol. I don't have any real reason besides the band wagon and being a sun bro. Praise the Sun!

I really love Bill from the game Left 4 dead.

Stephan Bekowsky from LA Noire for sure.

That is a hard one. The Last of Us is the only ine with truly memorable side characters for me. Or maybe Zeke fro. The Infamous series. There are just so many.

From Fallout, Joshua Graham from Honest Hearts. Speaking as an atheist, I found his internal moral struggle, even in the context of his religion to be fascinating, and quite frankly, if he were real, I would love to meet him and have a long talk about morality and life.

From Fallout mods, Russell, he is complex and interesting.

From not Fallout, HK-47, Tali from Mass Effect, and Fall-From-Grace from Planescape Torment

From the modding scene in New Vegas, I'd have to say Bobby Bass. A delightful gentleman through and through. From other games, Ciri from the Witcher and Morte from Planescape: Torment are both extremely well-written characters with endearing personalities.

Quiet MGSV, stone cold killer, aesthetically pleasing. Leave it to Kojima for finding a logical reason to fight in a bikini. Shame she can't talk

The Master, Joshua Graham, Ulysses, Edward Sallow, and Chief Hanlon are among my favorite characters in the Fallout universe.

I also have a soft spot for Tiny Tina from Borderlands 2.

I definitely have to go with Ulysses for Fallout.

From other games? I will have to go with Mikhaila Ilyushin from Prey. I don't want to spoil it too much for people who haven't played Prey yet (it's an amazing game) but her whole story arc with your character was really interesting.

Ulysses.
He has depth like no one else in NV, but that might just be because he has a lot of dialogue so we can get to know him.
He's perhaps the one person we can truly get to know and understand on a personal level.

H-H-Hey my man! T-T-Ten of Spades!

He seems so eager to earn his moniker (can't remember what it was), and that stutter probably got him bullied and shit, but hey, he made it into the top sniper unit in the NCR

@"Dmitri2033" and he had the glasses thing didn't he.
I think they called it it his "training shades" lol

Minsc and Boo from Baldur's gate 2, i will never be tired by those two!

in the Fallout series...while i think Ulysses is great i can't stop thinking that the greatest one of them all it's Harold, the human turned into a ghoul looking mutant that will became a tree that eventually will heal the soil of the Washington D.C. Wasteland!
He will meet and help the Vault Dweller (fallout), the Chosen One (fallout 2) and the Lone Wanderer (fallout 3), appearing also in Fallout: Brotherhood of steel

http://fallout.wikia.com/wiki/Harold