Has anyone else ever had this encounter before? I did on my first play through, probably about 15 hours or so into it. I encountered a 'Mercenary' along with someone else (can't remember their designation, but I don't think it was Mercenary) on the western bank of the pond that's just to the north of Sunshine Tiding's Co-Op. He didn't really engage in any dialog. He just made a comment along the lines of: "Move along, we don't have whatever you're looking for. Maybe you'll find it in Vault 81." This seemed like an incredibly odd and totally random comment. After the encounter my map updated to show the location of Vault 81. I never encountered him or any other 'mercenaries' again after this at any point in the 350 hours of my first play through. I hadn't yet encountered any Gunners at this point, but he was dressed like a higher level gunner for the most part. He was wearing army fatigues, and a full suit of combat armor, with the combat armor helmet.

I just started my second play through a few days ago (just hit level 16), and I was hoping to encounter him in this same spot. Unfortunately I didn't. My main reasoning for wanting to encounter him was to...ahem...kill him and take his combat armor. During my first play through I didn't realize the value of this armor, especially given how early in the game it was. I'm currently rocking full leather armor, and I just picked up my first pieces of metal armor a little bit ago, so once I get a full set put together I'll be upgrading to that. Obviously that combat armor would have been a huge upgrade. I was disappointed that I didn't see him.

I've searched online several times, and I haven't even been able to find mention of this character aside from a couple of wiki pages with no actual information about him/them. Who else has had this encounter? Are there more than one of the 'mercenaries' or is this a one time thing? Does anyone have any more information at all about this character?

These are the only two sources of information that I could find...and like I said, there's no information aside from an acknowledgment that they exist.

http://fallout.wikia.com/wiki/Mercenary_%28Fallout_4%29

http://fallout.gamepedia.com/Mercenary

Hes a Part of Covenant Mission. Hes around there, check the Streets

I've done all of the Covenant quests. Are you referring to the quest with Honest Dan? If so, that's not who I'm referring to. The 'Mercenary' character definitely wasn't in Covenant. This person was simply named 'Mercenary.'

After thinking about it some more, I remembered that I did see some more of the 'Mercenary' characters guarding the Parsons State Mental Asylum during the Jack Cabot quest line.

I haven't stumbled across this encounter before, but I am being relentlessly pursued by some guy wanting to sell me his dog.

More mercenaries can be found

I ran into the dude last night south of Diamond City, also headed to Vault 81. His name is http://fallout.wikia.com/wiki/Fred_O%27Connell.

Yes, I actually remembered this and mentioned it a few comments up.

That was one of my favorite quests. I had been looking for Combat Armor Helmets like crazy prior to that quest. I was outfitting my favorite companions with full combat armor, but I was having a really hard time finding the combat armor helmets. That quest netted like 6-7 of them. It's just a really cool quest aside from that too. They do remain non-hostile as long as you don't do anything to obviously provoke them.

You should buy it! You can send the dog to your settlement and it raises your defense by 5 points. Plus I just like having a friend for Dogmeat to hang out with. You can have this encounter multiple times too, so you can just keep getting more dogs if you want.

Good to hear that I'm not alone in encountering this guy. Hopefully I run into him sometime soon. I might decide to not kill him when I see him. I'll be tempted though. Combat armor is by far my favorite in the game, and I'm anxiously awaiting getting some more. I have a few hundred full suits in my first play through (minus the helmets) that I used to equip all of my settlers at my main settlements.

It is a random encounter, they are not uncommon, but there are a huge number of variations, so you don't have great odds of seeing most of them repeat.

I came across two mythic deathclaws in a duel to the death at level 50, one established it's dominance and they proceeded to go kill all the mutants at big john salvage.