I've found another good way to do this is by taking an NPC or two, or three, and having them intersect with the group and travel with them for a while, make connections, and disappear again. You can give them their own adventures and background and have them show up now and again either by coincidence, or by design.
My best example would be an NPC rogue who first used the PCs as involuntary bodyguards and got them to indirectly take down opponents- mostly by using them as a metaphorical battering ram. If the campaign had continued, she'd have appeared and disappeared with her own goals, with growing respect for the PCs and an interest in making deals with them as opposed to using them as dupes. Which would ultimately lead to a situation of being highly reliant on the PCs, and being eclipsed by their abilities.
I think it's also worth noting that adversarial relationships between NPCs in the party don't generally work out well. Or at least it hasn't happened to my experience. I've seen people get annoyed because they think the plot is revolving around these NPCs rather than themselves.
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My best example would be an NPC rogue who first used the PCs as involuntary bodyguards and got them to indirectly take down opponents- mostly by using them as a metaphorical battering ram. If the campaign had continued, she'd have appeared and disappeared with her own goals, with growing respect for the PCs and an interest in making deals with them as opposed to using them as dupes. Which would ultimately lead to a situation of being highly reliant on the PCs, and being eclipsed by their abilities.
I think it's also worth noting that adversarial relationships between NPCs in the party don't generally work out well. Or at least it hasn't happened to my experience. I've seen people get annoyed because they think the plot is revolving around these NPCs rather than themselves.