As yesterday, I've thought back over the various NPC's who've recurred in the games I've loved. I kinda wanted to pick a villain. Irrevetti, is the one who stands out because I hate him, and I'm loving it! He mostly recurs through being mentioned rather than us interacting with him, though, and I want to pick someone we spend in-game time with.
Irrevetti is a major villain in our Pathfinder game. The GM, Rich, created a bunch of NPC's and gave life to others from the book - to the point I'm not always sure which are which. From there, he expanded it to give Bells and I a full superteam of NPC's, as well as family, friends, mentors and rivals in Aberrant. I was really tempted to pick either Holly or Alastair from that game, for the maternal relationship Chrissie has with them both (most complicated with Alastair), but in my opinion it was Exalted where all the effort he's put into NPC building and development really came together. Again, some of them are named in the setting and many more are his creations - including some (Lawrence) who were created on the fly in response to things we chose to do (hire a child to help us not fall foul of curious and changing laws in a new city).
Meredith is wonderful. A First Age Solar living in seclusion, a Twilight, a formidable sorceror and crafter, she's scatty, she swears a lot, and my character idolises her more than a little. 'Gruncle' Cathak Chow, who raised the twins, last seen when he saved their lives in a part of the story not yet told. Captain Ling, another character who was created on the cuff and we liked so much (because she kept the young twins safe) she was used as a reason to get us to go somewhere dangerous...
But I'm going to pick the Undying Fury of Creation. If you've followed the story, you'll have met him very briefly in the 'non-canon' section. He's another being from the First Age, and carries his emotional baggage far more clearly than Meredith. A powerful Lunar, his bond with his Solar mate was such that her death tore him apart and he's never quite recovered. As mortals, Taji and Kito caused him great harm, such that Taji feels she owes him her death - that her death can come at no hands but his (though she still puts herself in thoughtless, reckless danger). As Exalts, he's saved her life on more than one occasion. Their relationship is complicated, emotionally intense, and very rewarding.
If you're taking part in the challenge, don't forget to leave a link to your response in the comments :)