Much like Carter Lockhart, I too am playing a character to help flesh out my 3 man party. This time I'm playing Meeka, the Tiefling Urban barbarian to be a main tank. Meeka has a rather unique reason to be apart of the Silver Ravens: she's promised one of our PC's late parents that she would look after the bard who likes to get himself into trouble. I do this to try to mitigate the npc from being a full-out McGuffin who has all the ideas/answers, so Meeka's only real motivation is to make sure that the bard and his friends don't get themselves killed. I have a couple of other npcs to cycle through if Meeka doesn't have a use/role to fill.
One of my other characters is an adapted character I played (as a player) in Skulls and Shackles who is a Halfling Inspired Blade Swashbuckler (Pirate captain) who is a very active member of the Bellflower network and has a very real interest in helping reestablish the network's presence in Kintargo.