Mercurius
Legend
What I mean is a frequently used NPC that either is an ally or even a member of the party. Obviously it is just an NPC, although if it is a multi-DM campaign, I suppose it could also be the DM's PC when they play. In the past I have sometimes used such an NPC, whether to flesh out party ranks, to be a source of information or guidance in some way, or just add a bit of regular interaction.
How have you done this? Again, I'm not talking about the countless NPCs - even frequent contacts - that the PCs will encounter, but one that is either a member of the party, or perhaps regularly drops in and out of contact. Are they just another party member or do you use them as a source of info dumping when necessary (e.g. Gandalf), or somewhere in-between? What problems have arisen? Etc.
How have you done this? Again, I'm not talking about the countless NPCs - even frequent contacts - that the PCs will encounter, but one that is either a member of the party, or perhaps regularly drops in and out of contact. Are they just another party member or do you use them as a source of info dumping when necessary (e.g. Gandalf), or somewhere in-between? What problems have arisen? Etc.