So yeah. Who exactly is this guy? He seems to test Johns morality all the time. I've been looking around and people have suggested he is God/Satan/Angel of Death/Grim Reaper. Because of quotes such as..
 
 John: "damn you"
Mysterious Stranger: "a lot of people have" 
 
And him saying he is an accountant..of sorts.
Also, John apparently tries to shoot him, but all of the bullets seemingly just go through him.
 
And I have not beaten the game, but apparently he is in the ending scene standing behind the people who kill John. (I know what happens in the ending, a guy spoiled it for me :( I don't mind though, I usually have games spoiled for me before they even come out.)
 
So yeah. Who do you think he is?

" When I first played the game I didn't notice the guy because I didn't do his quest but now I think of it, he was there. but, how many missions does the guy give you? "

" @CL60: Is he at the same spot for all his missions? "

" @JoeRiccadonna said:

" @CL60: Is he at the same spot for all his missions? "

 No. He starts in New Austin, on the side of a cliff. Second time he is in Mexico. "

Hmmm, never noticed him behind the guys who shot John. He looks a lot like the governement people though, so mabye it was just one of them?

I figured he was Death, fate, or something supernatural like that. Since John tries shooting at him 3 times at point blank range and didn't hit him.

" I figured he was Death, fate, or something supernatural like that. Since John tries shooting at him 3 times at point blank range and didn't hit him. "

" not only do you not hit him, he also just dissapears. "

" @owenneil said:

" not only do you not hit him, he also just dissapears. "

Really? "

" @CL60 said:

" @owenneil said:

" not only do you not hit him, he also just dissapears. "

Really? "

Pretty much yeah. "

I figured he was Satan but he wasn't very antagonistic. 
The way he gave you a choice whether to encourage his "friend" in thieves' landing would suggest he might be.    

I thought of him as John's past, coming back to him. I think it was Rockstar saying he couldn't escape his past, hence the (ENDING SPOILER HERE) 
Btw, which choices did you guys make? I made both good choices

" I thought of him as John's past, coming back to him. I think it was Rockstar saying he couldn't escape his past, hence the (ENDING SPOILER HERE) 
Btw, which choices did you guys make? I made both good choices

SPOILER WARNING: Click here to reveal hidden content.

shootout at the end, with him watching.

"

well im finishing psychology class, so i thought it was one of those cases of schizophrenia where they actually see people that aren't there, like in the movie Beautiful Mind
 
but yah i him being God or grim reaper seems likely too, very symbolic, i like the literary aspect

I like the God theory based on his dialog line that was: 
 
John " Damn you!" 
Man "Some have" 
 
As in Goddamn.  Just a thought.

I pushed him down a cliff once. Watched him tumble real good.  
 
That's what I do to shit like God and the Devil. Push 'em off cliffs.