Upon first visiting Vault 81 I met a guy in the central atrium who told me he would buy any tools from me for a reasonable amount of caps (think it was 25 caps).
Later I was unable to find him and I browsed the vault multiple times. Then on my second playthrough I did not even meet this NPC in the first place.
Do you guys know where he is or who he was? What are the conditions of his appearance?
Since I first met this character I completed the quest "Hole in the Wall", so I suspect he bugged out or something (similar to Dr. Penske's fertilzer bug). But this would not really explain why I did not meet him on my second playthrough.
Best Answer
It is a bug. He has teleported or otherwise removed himself to a hidden room near the vault entrance, which can be seen on the map but cannot be accessed without clipping through the wall.
I'm sorry I cannot find the original thread where I saw this discussion, but you can see the room on the map and of course can clip into it on PC to see for yourself. PC users can also of course use the console to move him back into the vault proper.
However those of us on console will simply never see him again, unless they patch him back in for us. :(
Oh and he isn't the only resident of vault 81 that can get stuck in that room. I'm missing 3 named residents in one of my saves, ugh...
Edit: Finally found a reference, though it isn't as detailed as the original I am thinking of it does specify the location better than I remembered: