I have six characters, and have never encountered the traveller. They are 57, 38, 21, 16, 7, 3. Rule out the last two because they are below level 10. How can I get him to spawn instead of the standard group of them. Where abouts do they spawn in what city? What time?

What mysterious traveler? Does he come with the add-on?

I've encountered him numerous times. Only during daylight hours. Only during the main DG quest. Only in cities, towns or smaller settlements (farms, even). And only in playthroughs where I've sided with the Dawnguard.

I only met him once. I was stepping out of the castle in Riften, it was daylight, and he was hanging out at the bottom of the steps.

It, like the vamp attacks, is completely random. I have only encountered the MT once, in the Riften market. I came in throught the front gate and he spawned in the middle of a cluster of townsfolk. They promptly took him behind the woodshed.

Riften, daylight? Everytime I enter a city I scout around it, and I have never found it. Oh well, I will just have to keep trying.

Have you ever done one of the DG radiant quests where you have to find a vampire impersonating someone? The mysterious strangers didn't start appearing until I completed one of those though I'm not sure if they're connected. Try it out

Ironically that's exactly when I saw him. I had just finished killing the vampire in the castle at Riften, walked out and there was the stranger.

I encountered the Traveler in whiterun about 1 every 3 visits there when I was completing the main questline for Dawnguard. I tried to stay away from other settlements/towns and cities during that time. He would only appear at night and I'd find him between my breezehome and the blacksmith shop. He wears a dark robe and hood unlike anyone else in Whiterun making him easy to spot. I just killed him on sight. The guards didn't care. I'd draw my sword, run up and take his head before he had time to cast a spell or call others. never lost a NPC on my play through of the MQ.

Keep in mind every time I spotted him, I had fast traveled.

ahhhhh.....you just solved the mystery for me! I had just enter Riften and was still standing by the gate when I heard a commotion and saw the villagers chasing after someone--couldn't figure out what that was all about and no one said anything either. Thanks!

NPCs will not attack the traveller until combat with the player is begun. He and they will just walk around as if nothing is amiss. Combat only begins when you get near the traveller. At that point the other NPCs will turn hostile to him, but not before.

If that happened in Riften it could have also been the ubiquitous "thief". The thief getting chased and "sentenced" by the guards is a relatively common occurrence there.