Places and things are not important. Only people really count. Therefore the most important thing you can do to make your RPG unforgettable is to make the people in it, the NPCs, memorable. Here are a few tips to accomplish this:

1: Let the PCs decide who is important.

You may have a plan to introduce a lovingly crafted NPC with lots of RP and adventure hooks but if the PCs don’t take to them then they are useless. If you ram a NPC down their throats it is just another form of railroading. Give the PCs lots of NPCs to meet and then fill out whichever ones they latch onto. Let the players’ interests guide who you develop.

2: Make sure you have a good name.

Nothing hurts a NPC more than being introduced as ‘Bob the whatever.’ Even if you try to rename them later they still will be ‘Bob’ to the PCs. It is another reason I bring a list of names appropriate to the setting with me to every adventure I run. A good name also means something the players can pronounce and remember. If you introduce your NPC as ‘Ithigulalweczys the Archmage’ the PCs will just call him ‘Sparky’ or ‘that wizard guy’.

3: Define their purpose in the narrative.

NPCs are agents of the plot and as such should have a particular role in mind. Are they there to help the PCs? To hinder them? Are they there to help move the plot or just for window dressing? These roles are not static. They can be changed by situations and PC actions.

4: Give them a personal goal.

What get s the NPC out of bed in the morning? What motivates them? This should be nice and general, like ‘Money’ or ‘Patriotism.’ Giving them a trait like this will help you cope with their reactions to unsuspected situations which players are so good at causing.

5: Stat out what you need to but don’t waste time on extraneous information.

The temptation is to not stat out the NPCs. They’ll do whatever they need to. What does it matter what their stats are? First off using a stat-less NPC can be disconcerting to the PCs unless of course you are real good at faking it. I’ve also found that if you have no stats on a NPC there are many judgment calls that have to be made every time they interact with the world. However you do not need tons of stats. Choose a couple primary skills that they are specialists in, 1 or 2 significantly high or low stats, and hit points in case the PCs try to kill them (or ‘miss’ with their fireball.) 

6: Choose your mannerism carefully.

There is almost nothing better than a quirk or mannerism for making a NPC memorable. Be careful though. You do not want to use duplicate mannerisms. Duplicates will cause confusion and blending in your players heads. To further complicate things if you ae throwing a bunch of NPCs at the party to see who they are interested in you may end up burning a mannerism on a ignored NPC.

7: Be careful what you steal.

Using real world personalities or fictional characters as a base for NPC personalities is a great shortcut however you need to keep the influences small. Avoid using names because that is the biggest giveaway. If the NPCs are too close to well known characters then it will distract the players and potentially give away plot development.

8: Keep them busy.

While the PCs are away the NPCs will play. NPCs should do things when the PCs aren’t around. PCs tend to spend a lot of time traveling. If they return to a place after a year or two the NPCs they knew should not be doing the same old same old. It works really well if they have been doing things either suggested or inspired by the PCs. The PCs will expect them to be doing the same thing they left them so it I nice to throw them a curve especially if it is their ‘fault.’

9: Keep them distinct from the PCs.

It is always tempting to have a favorite NPC join the PCs in their adventuring. This leads to the dreaded GMPC. If the NPCs do travel with the PCs they should never overshadow the PCs unless it is for a specific reason in the plot. Remember it is the PCs world. If you have NPCs taking the spotlight then really you are just playing with yourself.

Here is an example of a NPC done right: I once played in a campaign with a NPC named Savarish. Savarish was a traveling merchant who hired us adventurers as guards for his caravan. He was transporting lumber to the desert. He was from a Al-Qadim adaptation so he was exotic and interesting. As we traveled with him he would tell us stories of his homeland which inspired us. After we finished our journeys with him we had many adventures in the area and kept coming back to him for advice and help. This in itself was very remarkable because we were a very chaotic party (almost to the point of ADHD.) So the deep attachment we made to Savarish was an exception not the rule. We relied on him and trusted him almost more than we did each other. He even used us occasionally to further his own ends and we never held it against him. I don’t remmebr all the PCs names from that campaign but I remember Savarish.